The synthesis conditions of HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane) in Bachmann method have been researched. Ratios among reagents have been researched quantitatively to obtain high yield of HMX. When reaction temperature is fixed at 44 + or - 2°C, time of pouring materials is fixed at 30 minutes, retention time is fixed at 0 minutes, CH3COOH = 390 ml, acetic anhydride = 320 ml, then the quantities of other reagents: NH4NO3 = 108.8 g, HNO3 = 80 ml, HNO3 concentration = 99.5 percent, paraforrnaldehyde = (2+3) g will give highest yield of HMX, approximately 56 percent.