With the gradual increase in the depth of phosphate mining, the strength of the filling body under the filling mining conditions becomes increasingly higher. How to rationally design the strength of the filling body is a problem confronted by most mining areas. To rationally design the strength of the filling body, a method combining on-site measurement in the mining area and numerical simulation was employed to conduct real-time stress monitoring of the cemented filling body in the stope throughout the entire time sequence (filling stage, curing stage, and bearing stage), thereby obtaining the evolution law of the internal stress of the filling body. Numerical modeling and analysis were carried out using the real stratum information of the mining area to analyze the stress evolution law of the filling material from entering the stope to solidification and load-bearing throughout the entire process. By comprehensively comparing and analyzing the data of the numerical simulation and the on-site fiber Bragg grating stress sensor, a contrastive analysis was conducted on the evolution of the mining stress of the filling body throughout the entire time sequence. The on-site measurement results indicate that the filling body is a passive bearing entity. Only after the pillar adjacent to the filling body is mined through blasting does the filling body gradually start to bear the load. The internal stress within the filling body on one side of the pillar after its mining reaches 0.714 MPa. The numerical simulation results show that the internal stress within the filling body on one side of the pillar after its mining reaches 2.0 MPa, and when both sides of the pillar are mined, the internal stress within the filling body reaches 3.0 MPa. The filling body with a 28-day design strength of 3.0 - 4.0 MPa adopted in the mining area can withstand the corresponding disturbance, and the filling body is in a safe state.