Abstract: Before the S206 fully mechanized caving face in S2 mining area of changcun coal mine, the roof is weakened by direct charge pre-splitting blasting, and the initial pressure step distance of the basic roof is 17.6m. It is known from the analysis of the crushing radius that the roof pre-splitting effect is not good. In order to further shorten the first compressing step distance of fully mechanized caving face, taking the adjacent S208 fully mechanized caving face as the engineering background, according to the analysis of seam forming mechanism of cumulative blasting, a kind of cumulative charging structure was studied, and the characteristics of cumulative blasting were used to improve the effect of roof precracking. Then ANSYS/ ls-dyna numerical simulation was carried out to analyze the pre-splitting effect of direct charging and shaped charge blasting from the stress cloud diagram, crack radius and pressure-time history. It was concluded that shaped charge blasting has shaped charge effect, and the pre-splitting effect is better, which can weaken the roof and guarantee the safety of the initial mining period. In the end, S208 fully mechanized caving face has the first compressing step distance of 15.2m, which reduces 2.4m and improves the primary recovery rate. It has good economic value and application value.