Gruneisen parameter plays an important role in describing states of materials, especially for highly condition-depended detonation process. Herein, this key empirical parameter of unreacted plastic bonded explosive (PBX) is determined by a multiple shock-reverberated technique. The explosive sample is sandwiched between copper plates, within which, shock waves reverberate and compress explosive continuously. This rapid dynamic process is verified by the stepped pressures measured by embedded PVDF stress gauges. The Mie-Gruneisen equation of state is utilized to calculate the off Hugoniot reverberated states, which have a better agreement with experiments compared to the impedance match method. Five shots of such explosive produce enough experimental data to fit the most reliable Gruneisen parameter. This work demonstrates the accuracy of the shock-reverberated technique applied to insensitive explosive to determine Gruneisen parameter and provides reference for further study on unreacted JB-9014.