The effect of different ratio of PNP to PVB and different solvent in binder on the combustion beha-viors of heat-resisting caseless ammunition was studied by using the manometric bomb test. The experimental results show that the mixed solvent containing ethyl methyl ketone in the binder can enhance the combustion rate of the caseless ammunition,and the properly enlarged ratio of PNP/PVB can improve the combustion behavior as well.