In order to improve the battlefield decision-making ability of space commanders and ensure the timeliness of their decision-making, the uncertain situation fusion of space missions is studied. The concepts of space situation fusion are analyzed, and the space situation fusion is divided into 2 modules according to its characteristics: the deterministic situation fusion in the lower fusion layer and the uncertain situation fusion in the higher fusion layer. Aiming at the high fusion layer of space situation, an uncertain situation fusion method based on Bayesian network is proposed, and the mechanism and process of situation fusion are studied, and the method is verified by taking space emergency launch mission as an example. The results show that the research can support space commanders to make correct command decisions in the space battlefield.