A quasi-isentropic compression loading technique (ICE) driven by electro-magnetical was applied to investigate the dynamic behaviors of an un-reacted HMX based polymer-bonded explosive(PBX). Multiple samples with different thicknesses were loaded up to 8 GPa. Particle velocities of the interface between sample and LiF windows were measured by laser interference method, and by Lagrange data processing, the experimental isentropes within 8 GPa of this explosive were obtained. Based on the fitting parameters of the isentropes, the isentropic compression procedure was numerically simulated by one dimensional hydrodynamics code, and the calculated particle velocities are consistent with the experimental results.