The pressure recovery system is one of the key techniques for the high energy chemical lasers. Total pressure losses affect the key specification of lasers, such as the output ability, the size and weight of laser systems. The total pressure losses for combustion-driven continuous wave DF/HF chemical lasers were proposed according to the theory analysis of one dimensional gas exhausting. The analysis of the main factors of total pressure losses in the gain generator of the laser is the foundation of the research of recovering the gain generator with high pressure. Two major factors of total pressure losses caused by viscous friction and the temperature rise caused by chemical reaction in optical cavity were discussed in this paper. The result shows that temperature rise caused by burning has obvious influence on system′s performance of pressure recovery.