Equation of state of detonation products for HMX explosive is calculated. Detonation velocity and detonation pressure at CJ point are calculated as initial density of HMX explosive is 1.90 g·cm^-3. It shows satisfactory agreement with experimental data. Mole numbers of various detonation products are predicted and compared with results of BKW and LJD. Pressure, γ and mole numbers of detonation products along CJ adiabatic expansion path are given. They are helpful for understanding phenomenon of detonation.