With fuming nitric acid (95%) as the nitrating agent, six water magnesium nitrate as assistant, process improvement exploration was carried out for the synthesis of high energy explosive hexogen (RDX) by direct nitrolysis of urotropine. Based on the direct method, three main factors on the yield of RDX were investigated, such as the effects of the amount of Mg(NO3)2?6H2O, reaction temperature and reaction time in maturation period. The optimum synthesis conditions were obtained, which are: molar ratio of Mg(NO3)2 ?6H2O to HA: 1︰2; the temperature of maturation period: 30 oC; the reaction time in maturation period: 60min. The optimized process can improve the yield of RDX to 80.6%, 8.6% higher than the original process.