This actually depends on how you frame it. According to the doctoral students around me, there are generally no less than five chapters, and each chapter has to be subdivided into many small chapters. As far as chapters are concerned, there should be at least several chapters such as introduction, literature review, methodology, analysis, discovery and discussion, and conclusion. As far as the number of words is concerned, there is no hard and fast rule in China. Generally speaking, the number of words for doctoral dissertations is not less than 50,000 words for engineering and 80,000 words for liberal arts. But generally speaking, the writing of doctoral thesis needs to be higher than these words, otherwise you may fail to take the exam and take part in the defense, thus delaying graduation, so you must write more on the basis of this word limit.