Aiming at the problem that the blasting effect is not good due to poor or even no stemming of blast holes in underground coal mine,numerical simulation was used to analyze the mechanism of rock breaking and stemming mechanism.A 3 m×3 m two-dimensional concrete model with blast hole diameter of 0.04 m and hole depth of 1m was established using the finite element analysis software.In addition,the continuous emulsion explosive charge was set as 0.3 kg,and the stemming material was set as sand.For the explosive simulation,concrete and sand were modeled by Lagrange grid,and the air was modeled by Euler grid.ALE algorithm was used to simulate the explosion stress nephogram and damage cloud maps with a single hole stemming length of 0 mm,200 mm and 400 mm respectively under the blast load.The results show that the maximum stress around the hole with stemming is significantly higher than that without stemming.Meanwhile,the damage degree around the hole with stemming is more severe with smaller fragments than that without stemming.On the basis of analyzing the advantages and disadvantages of clay and water stemming structures commonly used in underground mines,a stemming structure by expansion-pipe water injection was designed,which can replace the clay and water stemming structure in underground coal mine blasting as a good field application.