Abstract: In order to reduce the roadway deformation of gob-side entry retaining and determine the size of the support resistance roadway-side back-filling, we utilize theoretical calculation to determine the length of key block and the roof-cut resistance of hydraulic prop, and establish the mechanical model of key block, analyze the surrounding rock deformation and the stress distribution, find out the relationship between fracture structure and key block by numerical simulation software. The results show that selecting 0.6 MPa support resistance in controlling the deformation of roadway has a significant effect according to the location and the characteristics of hard roof conditions and key block in coal mines.