Performance analysis of the Pulse Detonation Rocket Engine (PDRE) is numerically conducted focusing on partially filled system. Initial explosives, inert gas species, tube fill fraction, and equivalence ratio are chosen as parameters to clarify their effects on the performance of PDRE. The simulation results are compared with previous studies that used several explosives, and agreed well with them. The simulation results indicate that the initial mass fraction of explosive to the total mass is the dominant factor for the normalized I_<sp> under arbitrary conditions. We newly propose the partial fill model to predict the performance of partially filled PDRE.