Abstract: This paper, by using the method of data basis analysis, compared with the report of the 19th CPC National Congress with that of the 18th CPC National Congress, the "Decision on Deepening the Reform in an All-round Way" and the "Decision on Comprehensively Governing the Nation according to Law" adopted since the 18th CPC National Congress, and comprehensively and systematically explores the theoretical origin, policy evolution, basic connotation and historical significance of Xi Jinping's legal thought on socialism with Chinese characteristics for a new era as an important part of Xi Jinping's thought on socialism with Chinese characteristics, for the purpose of pointing out the important theoretical and practical value of Xi Jinping's legal thought on socialism with Chinese characteristics for a new era in the perspective of comprehensively governing the nation according to law. On the basis of the appearance and distribution of the word of "law" in the 19th CPC National Congress, this article also points out the new ideas in the report of the 19th CPC National Congress which includes promoting the work of constitutional review, strengthening the Central Government's constitutional responsibility to the (SARS), intensifying rule of law protection of human rights, and promoting the organic combination of "three governance" with self-government, the rule of law and the rule of virtue in the countryside and improving the public's legal literacy and so on. These new expositions are of great value to the improvement and a very important supplementary role of Xi Jinping's legal thought on socialism with Chinese characteristics for a new era. In addition, by analyzing the historical process of the formation of Xi Jinping's legal thought on socialism with Chinese characteristics for a new era, the author points out that despite the fact that there is no verbal expression in the report of the 19th CPC NC such as "Governing the Nation according to the Constitution" and "Governing the Power according to the Constitution", construction of procedural mechanisms of constitutional interpretation, strengthening judicial guarantees of human rights and the promotion of publicity and education of law, the above-mentioned ideas are still important components of Xi Jinping's legal thought on socialism with Chinese characteristics for a new era. We must pay great attention to these issues.