1 The overall structure of the thesis The structure of the doctoral thesis in engineering is similar, with Chinese and English abstracts, introduction, main chapters, summary and prospect. However, compared with master's thesis, narrative content, mature content and content without theoretical depth generally cannot constitute a main chapter. In other words, each chapter of the main chapter should have the author's own innovation in it, otherwise it will not constitute the main chapter, but should appear in the introduction. The writing of the abstract is the epitome of the full text, which should generally include research questions (what to do? ), the significance of studying the problem (why? ), research methods (how to do it? As a result, what did you get? ), conclusion (How about it? ) five parts. As a doctoral thesis usually consists of several sub-questions, the first paragraph of the abstract should be an overview of the full text, clarifying the main research content, purpose and significance; The writing of each subsequent paragraph is similar to the abstract of a journal paper, which consists of contents, methods, results and conclusions. The main purpose of the introduction is to explain the significance of the research, analyze the present situation of the research, and thus lead to the research content. The general process of preface writing is to make clear the field to which the research content belongs, the purpose and significance of the research, and analyze which sub-topics need to be studied in this field, what is the research status and which are mature. What problems need to be solved urgently are our research contents. The introduction mainly includes the research background, the analysis of domestic and foreign research status, the main research content of this paper, and the arrangement of full-text chapters. The analysis of the present situation at home and abroad can not simply list the progress of various studies at present, but should specifically analyze the advanced nature and existing problems of various studies. Because this is the key to guide us to carry out research. 4. The title of the text should clearly distinguish whether this part of the content is the author's citation of other people's achievements or the author's own research achievements. If it is the result of others, the topic is generally adjective+noun structure, such as the basic theory of Petri net, BP neural network method and so on. If the author's own research results are expressed, the title is generally object+verb structure, such as maintenance process model construction, disassembly sequence planning method and so on. The main chapters of the text are written in the text.