To establish the Γ-Ψ expression of variable burning rate gun propellant with square plate-shape,the factors affecting its gas generation were analyzed theoretically. On the condition of geometric combustion law,the theoretical expression between Γ and Ψ were derived,taking the initial size,burning-rate ratios,and density ratio as the basic parameters. By theoretical calculation,influences of width-thickness ratios,outer-to-total thickness ratios,density ratios and burning-rate ratios on the gas generation rule were discussed. The results show that variable burning rate gun propellant with square plate-shape can control the energy release law by using the appropriate width-thickness ratios,outer-to-total thickness ratios,density ratios and burning-rate ratios. The brisance of gas generation increases by 2.6 times when the inner and outer combustion speed ratio triples.