In order to determine the reasonable thickness of the overburden in the first mining stage of the No. VI. ore body of Chengchao Iron Mine, theoretical calculations and numerical simulation studies were carried out. In this paper, considering the theory of ellipsoidal draining, the theory of gas dynamics and the requirements of mining technology, combined with the analytic hierarchy process, a method for calculating the thickness of the overburden layer weighted by the analytic hierarchy process is proposed, and the theoretical thickness value is obtained, and the following conclusions are verified and obtained by combining with the particle flow numerical simulation software PFC2D: ① the weight coefficient value calculated by the analytic hierarchy process is obtained, and the importance proportion of various theoretical methods is obtained: ellipsoidal drawing theory> gas dynamics theory > mining technology requirements; ② The overburden thickness value is calculated as 25.49m based on the weight coefficient assigned by the analytic hierarchy process; ③ The overburden thickness is 26m under the maximum ore recovery rate and the minimum rock mixing amount through the simulation of the overburden thickness by using PFC2D discrete element software. On this basis, combined with theory and numerical simulation, it is consistent with the reasonable overburden thickness recommended by China ENFI Engineering Technology Co., Ltd. to the mine of 26m, which ensures the safety of mine production and provides a theoretical basis for the realization of good technical and economic indicators.