If you google "英语摘要的时态，" you will see "use the past tense." (网上搜索，你会看到“摘要应该用过去时”。)If you never wrote a paper on your own, you may take this as the truth and follow it faithfully.But, I have to say this "rule" needs to be relaxed. Here is why. (但是，摘要不一定非用过去时哦。)
I am an ocean modeler, and used to write papers on basic physics related to ocean dynamics. I never used the past tense in my own abstracts, never. Instead, I used the present tense. (Oh, in case you don't know my work, all my papers were published in good journals in the field.) Why? This is because these papers are about basic physics, and the results remain true if one repeats these numerical experiments (at least I hope so :)
So, now you know at least there are two ways to write an abstract: the past tense, and the present tense. (摘要可以用过去时，也可用现在时。)
In fact, you cannot use the past tense if you want to end the abstract like this: "This new method has great potenial in xxx application." (有时你不能用过去时，比如谈论一个新方法的应用。)
The best way to decide which tense to use is to read your colleagues' papers and to check out journal's requirements (under guidelines for authors).(最好的办法是看看你的同行怎么写摘要、看看期刊是怎么要求的。)
One more thing, to end the abstract with the potential impact of some of your new findings, you have to use the present tense, I think. (Now, you see where I stand.) (显然，有时你只能用现在时。)
For example:This new method may have potential application in identifying new species.
I also find this link useful for Chinese authors:http://www.xuebao.tyut.edu.cn/webpage/EI.htm
In the introduction, we need to cite publications.(在引言部分，我们会引用一些发表的文章。)
These are common practice:
1) Use the past tense when a sentence starts with a publication. (用主动语态叙述已经发表的文章时，用过去时，不建议用现在完成时。)
Ren et al. (2015)noteda dramatic increase in publication by Chinese authors in SCI journals during the 2000s, thanks in part to the cash reward and promotion criteria set by the (Chinese) system.
Note that even though the publication is recent, I still use the past tense, “noted.”(大家注意到上面引用的文章还很新，是去年的。我依然用了过去时。)
Note also that I have no authority to make you follow this rule; but from now on you should pay attention to how your colleagues write when you read their papers. 2) Use the present tense for a result/fact that remains true today, even though the result/fact was obtained 100 years ago.(在叙述一个事实时，用现在时。)
The Gulf Streamis(用现在时，因为是事实)the most powerful western boundary current on Earth, whichwas discovered and confirmed(用过去时，因为已经发生了)bysailors and scientists hundred years ago.
3) Use mixed (say past and present) tenses in one sentence.(一个句子中的时态不必统一!)
If you don’t like the sentence I made up in 2), here is one from Wikipedia:
European discovery of the Gulf Streamdates(因为是事实)to the 1513 expedition ofJuan Ponce deLeón, after which itbecame(已经发生了)widely used by Spanish ships sailing from the Caribbean to Spain.
4) The last paragraph of the introduction maps out the paper. Use present tense.
It often goes like this:
The rest of this paper is organized as follows. In Section II, the procedure of the xxx method is presented. In Section III, the proposed method is tested using 66 images with different kinds of textures. Finally, Section V presents the summary of the paper.
Note that the last sentence is perfectly understandable for native and non-native speakers. In fact, most native speakers may not pay attention to the grammar (as they were never really taught the way we non-native speakers were). However, a non-native speaker editor/reviewer may pick on you, telling me that “Section V” is not a human with a brain to present something to the readers. What should you do then? Give in.
To describe the methods and datasets used in the paper, we can (and should) use the present tense.
We use the WOA (World Ocean Atlas) data as initial conditions for our numerical experiments. We use satellite data to validate model’s phytoplankton field in the surface layer.
别跟审稿人“一般见识”：我的一个同事被审稿人“教导”说，这些地方统统必须用过去时!You may say “Fxxx off. This is MY paper!” But, you should only say it to yourself loudly (or quietly). One should choose one’s battle, so let this one go.(不要为小事跟审稿人争。在这里用过去时无伤大雅。)
If you describe how you collected the data(过去时，已经发生了), however, you have no choice but to use the past tense.(观测数据采回来了，一定是今天以前做的事。对不起，必须用过去时。)
If you describe the procedure of processing the data, however, you may choose to use the past tense (emphasizing how you did it，用过去时，因为你已经处理了这些资料), or the present tense (illustrating how such a procedure should be performed，用现在时，示范如何常规地处理这些资料).
Figure 5 (or Table 3)showsx,y, andz. (一定用现在时，因为作者是在与读者实时对话。)
We use the present tense to describe all our (finished numerical) experiments. If you prefer to use the past tense, it is fine as long as you do soconsistently.(可以用现在时或过去时描述你的数值模拟结果。)Do not switch from the past tense to the present tense randomly.(不能太任性哦：一会儿现在时，一会儿过去时。)
Exceptions(不能任性的地方): To study present (modern day) climate, using the present tense is the ONLY way to go, I am afraid. (如果是研究现代气候，一般用现在时。)
If a sentence involves a specific time, such as June 2001, you need to use the past tense.(句子中提到过去的某年某月，那么，一定要用过去时。)
Figure 3shows (现在时)that Typhoon Megi (2015)moved(过去时)away from the coast suddenly.
如果你不喜欢这种“混合式”，可以这样玩： Typhoon Megi (2015)moved(过去时)away from the coast suddenly (Fig. 3).
Discussion and Conclusions
You may use the present perfect tense, such as “we have shown,” or use the past tense.Just be consistent.(任性的时候到了!但是，认准一个时态，不要朝三暮四哦。现在完成时、过去时都可以。)
Once again, you mayuse mixed (say past and present) tenses in one sentence.(一个句子中的时态不必统一。)
In this paper, weshowed (过去时)that the new indexis(现在时) capable of tracking algae blooms in spring.
虞左俊博士是物理海洋学家、自由撰稿人、高级英文编辑。毕业于山东海洋学院(海洋气象专业学士)、中山大学(热带气象专业硕士)和Nova University(现Nova Southeastern University，物理海洋专业博士)。她曾为世界权威科技媒体Scientific American的中文版《环球科学》校稿，也是加州大学伯克利分校David Sedlak教授所著Water 4.0: The Past, Present, and Future of the World’s Most Vital Resource一书中文版的校稿人。