In view of the fact that such factors as groundwater and supporting conditions will affect the stability of surrounding rocks after tunnel excavation in the process of the tunnel passing through the geological environment with developed joints and fissures, with a case study of a mountain highway tunnel in China as the background, based on the discrete element theory, an analysis has been made of the influence of such support conditions as mortar anchor and concrete lining on the stability of surrounding rocks after the tunnel excavation, with the effect of fracture water pressure taken into consideration, followed by a simulation test of the excavation and support of tunnel in fractured rock mass by using 3DEC software. The simulation results show that groundwater exerts a great influence on the excavation and support of the tunnel in fractured rock mass, with the overall and local displacement of the tunnel in fractured rock mass with groundwater 2~3 times higher than that of the tunnel without groundwater, and that the displacement of surrounding rock can be reduced by 20%~32% by adopting reasonable support methods under two different working conditions with or without the fracture water.