Abstract: In order to research the distribution law of the rock fragment size, five groups of blasting test were done, thus a number of data were obtained. According to the statistics and regression of these data, the blasting fragmentation distribution function was found. There is a certain relationship between parameters x₂, n of the function and the rock fragment size after blasting, and the impedance matching degree of rock and explosive has great influence on the blasting fragmentation distribution. By the investigation of the factors affecting the rock fragment size distribution, the basis for the selection of size degree evaluation index was discussed, and the method in selecting the blasting parameters and explosive was proposed.