Ever since Japan established diplomatic relations with Central Asian countries in 1992，Japan’s Central Asia diplomacy has experienced four phases，and demonstrated a trend of continuous upgrading. There are many analyses on the reason for this upgrading. Compared with the more popular theories focused respectively on energy，economic cooperation and Japan-US alliance，this paper points out that the attempt to become a “political power” and “Asian leader”is the fundamental reason for the upgrading of Japan’s Central Asian diplomacy. Japan’s entrance into Central Asia is bound to present competition with China，but there also exist space for the two countries to cooperate in this area.