Abstract: The modernization of legal system is the course of transition and evolution in which the law and its system have been breaking away from ancient traditions towards modern civilization. Sun Yat-sen’s legal thoughts and practices involved a series of key subjects related with the modernization of legal system. For example, he proposed a systematic democratic republic constitution and carried out such great constitutional practices as founding the Republic of China, democratic constitutionalism, ensuring civil rights, etc. What’s more, he created a government by law instead of a government by men. He seperated Five Powers from each and held the idea of judicial independence. He objected to class privilege and claimed equal human rights. Besides, he changed the old traditions of all laws united into one. He objected to severe punishment and thought that criminal penalty should be accoding to humanitarianism. Therefore, we know Sun Yat-sen had great contributions to and profound influence on the modernization of Chinese law