After the end of World War II, since the surrender of the Japanese militarist Empire, Japan had political reform with the help of the United States. It was the beginning of Japan's diplomatic normalization after the end of militaristic diplomacy. Since the new century, from the “Follow America and give priority to economic development” to the “New capitalism and realism diplomacy in the new era” foreign policy with domestic and foreign coordination, Japan's diplomatic strategy towards China has handled resoundingly on the delicate relationship of competition between China and the United States. Japan has a lot of deep cooperation with the United States, Japan maintains a relatively harmonious relationship at the same time. This paper focuses on the important strategic changes in Japanese diplomacy from the beginning of the 21st century to the present and the leading ideas and lines of Japanese diplomacy in different periods. According to Japan's various strategic changes, domestic and foreign factors have proved that Sino-Japanese relations are both stable and fragile.