Abstract: The road way section size is very important in cemented underhand heading backfill mining for it relates to mining safety production. This paper studies the relationship between rectangular section size and stope stability using FLAC^3D based on practical engineering. The distribution of stresses, displacement, plastic zone are analyzed. The results show that the height of road way has little effect on stope stability. The stope will be in the critical state of instability when the span is 6 m.