Abstract: The determination of the fracture angle is critical to the design of gas extraction boreholes in goaf. However, The existing re-searches mostly stay on the basis of numerical simulation and similar material simulation, and lack effective verification of field measured data. Based on the actual situation of Shen Nanwa Coal Mine, this paper conducts an in-depth study on the development of the fracture angle under the condition of large mining height of composite roof. Through the long-term ob-servation of the high-level drilling extraction data, the fracture angle along the working face side is calculated; The lateral fracture angle of the goaf was studied by double plug water test; Finally, UDEC numerical simulation is used to analyze the evolution process of overburden mining fissures and fracture angles. Research indicates: when the surface advancing speed is 3.6m/d, the fracture angle of the working surface side is 59°, and the lateral fracture angle of the goaf is 58° at 100~110m behind the working surface; The fracture angle is in a dynamic process that will gradually change over time, up to 109°. The obtained research results can provide theoretical basis for the study of drilling arrangement and gas migration and enrichment in goaf.