Abstract: This paper analyses the situation of the cooperation of transboundary river between China and Southeast Asia from the geopolitical environment perspective. China and Southeast Asia cooperate closely in hydropower development，electric power trade， international channel， environmental protection of the four transboundary rivers. The cooperation of transboundary river between China and Southeast Asia has several problems such as the prospect is not optimistic, the pursuit of self-interest, water disputes, environment , immigration , ethnic and so on. Then focuses on the geopolitical environment impacts upon the cooperation of transboundary river. We can take these measures to optimize the geopolitical environment so as to promote the cooperation of transboundary river ：properly handle the sovereignty dispute，fully play the role of the regional cooperation organization，improve the public opinion environment，deal with the equilibrium strategy of Southeast Asia and the power intervention，set up the transboundary river cooperation mechanism，attention to sustainable development. The basic conclusions are: (1)The transboundary river have rich geo-economic and geo-political implications ; (2)The cooperation of transboundary river between China and Southeast Asia adequately developed, but there are still many problems ; (3)The geopolitical environment is an important fator affecting the cooperation of transboundary river that it has positive and negative influence on the cooperation; (4)China's strategic choice is that to promote the cooperation of transboundary river through optimizing the geopolitical environment.