Abstract: In order to find out the performance advantage of pulse detonation rocket engine over a rocket engine,the primary objective of this research is to compare the thrust and the specific impulse of PDRE based on constant-volume cycle model with a rocket engine with small thrust.The results show that at vacuum conditions,with the increasing of initial temperature,the specific impulse increase not obviously.If the propellants are same and the sizes are similar,the thrust of PDRE is 3.0~6.8 times more than that of a liquid rocket engine′s,while the specific impulses are equivalent.