Japan’s maritime strategy in the South China Sea is based on its geopolitical strategy depending on U.S-Japan alliance，with indirect involvement and limited direct engagement. In the aspects of diplomacy and security，Japan’s geopolitical strategy and the maritime strategy concerning the South China Sea are closely linked with each other，with geo-economic activity in that region contributing to a favorable diplomatic environment for Japan. Due to those characteristics，Japan’s maritime strategy is also faced with some constraints such as the uncertainty of indirect involvement，the divergence in the objectives and interests between U.S. and Japan，and Japan’s limited capability of direct engagement. If Japan enforces its maritime strategy recklessly，there will be counterproductive effect，damaging the security environment and doing harm to Japan’s own national interests.