In order to investigate the energy property of RDX/AP/Al/HTPB propellant, theoretical calculation is conducted. By the ignition experiment of BSF 165 mm and BSF 315 mm motor,We summarize the regularity of energy property with the change of RDX content in propellant and chamber pressure of motor. The optimum formulating is designed according to the results of theoretical calculation and experiment.The comparative tests by 760 mm motor have further confirmed the contribution of RDX in specific impulse, and the actual specific impulse is 2 428.1 N·s·kg^-1(p_c=6.86 MPa) of 760 mm motor.