The crystallization technology conditions of preparing the Reduced Sensitivity RDX (RS-RDX) by direct nitrolysis of 1, 3, 5, 7-tetraazatricyclo[3.3.1.1^{3, 7}] decane (HA) at the presence of 1-methyl-imidazole nitrate (ionic salt) were studied. The effects of stirring speed, crystallization temperature, amount of ionic salt, and dropping rate of water on the crystalline form of RDX were investigated. The morphology and sensitivity of RDX crystals were analyzed and characterized by scanning electron microscopy (SEM), and impact sensitivity test. The results show that the optimal crystallization technology conditions are the molar ratio of 1-methyl-imidazole nitrate and HA is 0.015, and stirring speed 800 r·min^-1, dropping rate of water 1 drop/40 s, crystallization process temperature 10~70 ℃. The RDX obtained under the optimum conditions is uniform with regular shape like octahedron, and the explosion probability is 17% according to the standardization method of GJB772A-1997-601.1.