The stability of unilateral exposed one-step filling body is the key to safe mining in the two-step mining. The stress and displacement at different positions of the one-step filling body in the 5371 stope of an iron mine were studied by means of numerical simulation and field monitoring. The results show that: ① The vertical stress of the measuring point at the bottom of the exposed filling body changes the most, about 0.48 MPa. The closer to the top of the exposed surface, the greater the horizontal displacement of the measuring point, and the maximum horizontal displacement is about 32 mm. ② The excavation rate of the two-step pillar is logarithmically related to the maximum vertical stress and maximum horizontal displacement of the exposed filling body. Different excavation times have little effect on the vertical stress at the bottom of the filling body, which is about 1.92 %. And, different excavation times have a great effect on the horizontal displacement of the top of the filling body, which is about 5.65 %. ③ The field monitoring results show that the vertical stress change in the middle of the unilateral exposed filling body is largest than that in the top measuring point during the two-step stoping, and the maximum value is 0.3 MPa. The maximum horizontal displacement occurs at the top of the filling body, reaching 30 mm, which is basically consistent with the numerical simulation results. The research results provide a guarantee for the safety of the two-step stoping of the iron mine.