Ao’baogou tunnel crosses underneath the roompillar goaf of Zhongxing Coal Mine. In the paper, the construction of Ao’baogou tunnel crossing underneath the roompillar goaf and the regularity of the construction mechanics and the deformation of the surrounding rocks during different tunnel excavation steps are simulated and analyzed by means of MIDASGTS. Conclusions drawn are as follows: 1) When the tunnel crosses underneath the roompillar goaf, the excavation of the roompillar goaf leads to the compression of the coal pillars and the significant horizontal displacement of the side walls and the coal pillars, and the influence extends the scope of 2 times the coal excavation length on the ground surface; 2) The construction of the tunnel crossing underneath the roompillar goaf increases the vertical displacement of the floor and roof of the goaf, which results in ground surface settlement within the scope of 3 times the excavation depth; 3) The deformation of the goaf, the coal pillars and the ground surface is closely correlated with the tunnel excavation steps, and the influence on the tunnel crown imposed by the deformation of the floor of the roompillar goaf is the main cause for the tunnel collapse. The study results have been applied in the construction of Ao’baogou tunnel, which guarantees the safety of tunneling underneath the roompillar goaf.