Abstract: Taking the roof support of No.3 stope in -400 m middle section of Liguanji Iron Mine as the engineering background，and comparing with the classification standard of engineering rock mass，the rock mass of No. 3 stope in -400m middle section is divided into Grade IV rock mass with poor quality. Through the analysis of the instability mode and mechanism of broken roof，it is determined to adopt the support method of resin bolt to strengthen the roof. Using FLAC3D numerical simulation method to analyze the stability of roof before and after stope support，the variation characteristics of displacement field and stress field of roof slate and the expansion law of plastic zone are obtained. The results show that after the use of bolt support，the movement and subsidence of roof strata are reduced from unsupported 32 cm to 16 cm，and the height of overburden plastic zone is reduced from unsupported 9.6 m to 6.4 m，which proves that this support method can effectively control the roof displacement，and the research results can provide reference for similar mine stope support.

Key words: broken roof, rock mass classification, suspension theory, resin bolt