In order to investigate the micro-crystalline structural morphology in Melt-cast explosive and improve the quality of explosive column, the CAFE module of ProCAST casting simulation software was used to simulate the internal crystalline structure of TNT melt-cast explosive. Using cellular automata in CAFE module, the shape and size of grain in column under different technological conditions and TNT nucleation parameters were predicted. The improvement measures of grain refinement process were obtained by adjusting the nucleation undercooling degree, pouring temperature and cooling rate of melt. The results show that with the decrease of melt nucleation undercooling, the equiaxed grain area in the column gradually increases, and the average grain size decreases to 458.5 μm from 715.5 μm; with the decrease of melt surface nucleation undercooling, the grain morphology inside the column does not change significantly, and the average grain size increases to 719.2 μm from 715.5 μm; with the decrease of melt pouring temperature, the equiaxed grain area in the column gradually increases, and the average grain size decreases to 729.2 μm from 1114.5 μm; with the decrease of cooling rate, the central equiaxed grain area gradually enlarges, the outer equiaxed grain area gradually disappears, and the average grain size increases to 1149.1 μm from 719.4 μm. After process optimization, the column is composed of fine equiaxed grains with an average grain size of 516.9 μm, the size distribution is concentrated, and the micro-quality of the grain is greatly improved.