Taking the backfilling stope of gently inclined thick orebody below the level of Chengchao Mine -675m as the research object, the two-step stoping of the target orebody is carried out by means of sublevel rock drilling followed by backfilling, so as to explore the influence of the span of different mine houses (pillars) on the stope stability. Three numerical simulation research schemes with different spans are formulated according to the theoretical analysis results, and the stope of different mine houses (pillars) with different spans is simulated and studied by using FLAC3D software. Based on the FLAC3D numerical simulation results, the stress, displacement and plastic area distribution of each scheme are compared and analyzed, and the optimal scheme is determined when the span of mine houses (pillars) is 15m. In order to evaluate the stability of the stope with a span of 15m, the monitoring data of vertical subsidence in the stope process are analyzed and sorted. The results show that the slope of the monitoring points near the important buildings (structures) on the roof is 0.77 mm/m, the curvature is 0.032mm/m2, and the horizontal deformation is 0.161mm/m.