Abstract: The measurement of expansion energy of initial released gas can realize the accurate prediction of coal and gas outburst. We studied the influence of many factors including gas pressure and particle size and moisture of coal samples on expansion energy of initial released gas by orthogonal experiments, which is based on the impact research of single factors on expansion energy of initial released gas. The results show that the influence degree of gas pressure, particle size and moisture on initial expansion energy of released gas reduce gradually; the influence of gas pressure on initial expansion energy of released gas is the largest; the determination of vacuum process can reduce the moisture value of original coal sample.