An investigation about the effects of burning rate bicatalysts on the pressure exponent of HTPB composite solid propellants over the range of 2.94～8.82 MPa was carried out by determining the static burning rate. The results show that in these propellants the pressure exponent was lowered with adding ferric oxide,ferrocene derivant,copper chromium compound,oxalate and bismuthous oxide and a optimal one of these is copper chromium compound which lowered pressure exponent by over 20%,and the capacity of oxalate is related with content. It was found that on lowered the pressure exponent there are a superposition and a preference between some bicatalysts.