To study the mechanism of advanced grouting reinforcement in fault fracture zone, based on the actual project of the Yangzong tunnel crossing multiple fault fracture zones, a three-dimensional numerical model of crossing fault fracture zone is established using FLAC3D software. The control effect of advanced small pipe grouting reinforcement with different thicknesses and grouting ranges on the surrounding rock of fault fracture zones is studied. The results show that: 1) The increase in the thickness of the grouting reinforcement layer has a significant control effect on the horizontal displacement of the tunnel, especially on the settlement of the tunnel arch. It also has a control effect on the horizontal displacement of the tunnel, but it is not as effective as the control effect on the settlement of the arch. When the thickness of grouting reinforcement layer is 1.5 m, the tunnel crown settlement and maximum horizontal displacement are reduced by 26.96% and 16.03%, respectively. 2) With the expansion of grouting range of the advanced small pipe grouting, the control effect on the horizontal displacement of the tunnel significantly becomes better, while the control effect on the vertical displacement has little change. When the grouting range is 150° is used, the tunnel crown settlement and convergence of the periphery are decreased by 26.62% and 22.80%, respectively. 3) The strength of the surrounding rock in the fracture zone of fault is enhanced, the deformation of the weak surrounding rock is controlled, and the overall stability of the surrounding rock is improved effectively through the reinforcement of the advanced small pipe grouting. The research findings provide a basis for tunnel construction on-site and are of certain reference significance for similar tunnel construction projects.