Abstract: In mine blasting mining，the constraint conditions of ore rock have a great influence on the blasting effect. Through indoor experiments，the influence of constraints on the degree of ore fragmenta⁃ tion under explosion load was studied. In the experiment，gravels with different particle sizes are used to simulate the constraints of free surface. The ore fragmentation after blasting is screened and counted，and the three-dimensional fractal dimension of fragmentation is calculated. The results show that the constraint conditions have an important influence on the blasting fragmentation distribution. In the case of the same amount of explosive，with the increase of the particle size of the constrained crushed stone，the non-uni⁃ form coefficient of the blasting ore fragmentation and the block rate show a trend of decreasing first and then increasing，and the fractal dimension value of the fragmentation shows a trend of increasing first and then decreasing. There is an optimal boundary condition，which makes the blasting ore block smaller and more uniform.

Key words: ore size distribution, constraint condition, mining blasting