Based on the engineering background of No.2303 Face in Changcun Mine, the empirical formula of ' two zones ' height, 3DEC numerical simulation and field measurement method were used to study the development height of ' two zones ' and the evolution law of roof stress in the process of fully mechanized caving face mining. Through theoretical calculation, the height of caving zone of No.2303 Face was 19.42 ~ 21.92 m, and the height of fracture zone was 57.43 ~ 75.23 m. Through the numerical simulation method, the height of the caving zone was 21.93 m, and the height of the fracture zone was 51.27 m. According to the field measurement results, the height of the caving zone was 11.86 ~ 26.02 m, and the height of the fracture zone was 57.12 m. The results obtained by the three methods were basically consistent, and the reliability of the calculation results was high.