Japan’s science and technology level can be ranked among the most advanced countries in the world for a long time, and it is inseparable from its relatively perfect scientific research evaluation system. Japan has enacted special laws on science research evaluation and the evaluation laws at different levels have promoted the improvement of Japanese scientific research level effectively. This paper analyzes the background and content of the laws and regulations at different levels on scientific research evaluation in Japan and studies the mechanism of legislation promoting Japan’s scientific research level. The study finds out that, firstly, the Japanese science research evaluation laws cover a wide range of fields and the system is complete; secondly, the formation of evaluation culture brought by sufficient legal foundation is favorable to promoting the development of scientific research evaluation system; and thirdly, the complete legal system and evaluation culture widely supported in the society have ensure impartiality and fairness for the Japanese scientific research evaluation process. 