The microstructure of two-layered variable-burning rate propellant was studied.The existence and characters of crazes were proved and the compensating mechanism of crazes was put forward.Using scanning electron microscope

we could observe the thickness of crazes changed with temperature;in the closed bomb test

compared the combustion characters of the treated propellant with that of original propellant

analyzed the interior ballistic performances at different temperatures on a certain shrapnel shell.By the changes of thickness of the crazes with temperature

the burning area of the propellant is changed and the desire discharge rule of the propellant is realized.The result indicates that the correct principle of crazes

the stability of crazes and the existence of crazes cause the two-layered alterable-burning rate propellant to have low temperature coefficient.