The present paper investigated the effect of some compounds on burning rate pressure exponent of HTPB composite solid propellant. The experimental results proved that CdS is a better additive for lowering HTPB composite solid propellant burning rate pressure exponent. When CdS Was used with other burning rate catalyst as a mixture additive，it may obviously lower propellant burning rate pressure exponent and enhance propellant burning rate. Final1y，we have used DTA technique to approach the action mechanism of CdS preliminarily.