In addition to polypropylene, acrylonitrile, and carbonyl alcohol, propylene oxide is the fourth major derivative among propylene derivatives and one of the important basic organic chemicals. A thermal stability test of catalyst, methanol, and hydrogen peroxide (H2O2) was conducted via differential scanning calorimetry (DSC). Propylene epoxidation with H2O2 over catalyst, methanol, and propylene evenly mixed by specific pressure was carried out, and then the runaway reaction under adiabatic conditions was further simulated by the vent sizing package 2 (VSP2) to measure temperature and pressure data with respect to time of the runaway excursion. Finally, the apparent activation energy of H2O2 and propylene oxide reaction was obtained via temperature variation equation to evaluate the degree of potential hazard in industry.