Abstract: In view of the change of coal seam occurrence in open pit mining in China, this paper establishes a 3d geological model, optimizes the design of the throwing blasting step based on the theoretical design, and calculates the height of the throwing blasting step corresponding to the thickness of each coal seam. This paper takes heidaigou open-pit coal mine from the first mining area to the second mining area as an example to optimize the design. The occurrence of coal seam changes, the thickness of coal seam increases, and the inclination of coal seam in the direction of working line increases. There is a fault depression zone in the north of the second mining area, which results in a large local change in the height of the throwing blasting step. In the field operation, the throwing blasting step height should not change frequently, and the front and rear amplitude should not change too much. On the premise that the coal exposure is not affected within the one-year period unit (about 4 pieces of advance), the height of throwing blasting steps is linearly balanced, the height of throwing blasting steps is slowly adjusted, and the top slope is adjusted to meet the slope requirements of the cone drilling rig.