At least 150000 words, generally no more than 200000 words. The doctoral thesis has been refined to1.5,000 to 200,000 words. If there is still a lot to say, it can be supplemented appropriately after the dissertation is passed, or it can be published as a monograph. Of course, the number of words in a doctoral thesis should not be too small, just like a simple outline, which shows that the author has not studied hard. It should be noted that the topic should not be too small or too big, and it is necessary to make a mountain out of a molehill, that is, a small topic and a big article. Small topics and big articles are not only conducive to full play, but also suitable for control, making the research results more solid. Good topic selection, although the topic seems small, but the depth and thickness are relatively large. When writing academic papers, research should go straight to the point, and not be greedy for perfection and blossom everywhere.