The prediction accuracy of tunnel water inflow in water rich fracture area is poor, and the problem of water inflow has not been well solved. To solve this problem, considering the fractured surrounding rock and grouting area as heterogeneous and anisotropic media, and the initial support and secondary support structures as homogeneous and isotropic media, a simplified calculation model of tunnel water inflow under fractured surrounding rock is constructed. The calculation formula of tunnel water inflow in water rich fractured area is deduced based on the theory of underground hydraulics and the law of fluid mass conservation. Through the degradation analysis and the field measured data of the case project, the rationality of constructing the simplified calculation model of tunnel water inflow in the water rich fissure area and the correctness of the solution of the calculation formula of water inflow are verified. Finally, based on the analytical solution, the influence law of each characteristic parameter on the tunnel water inflow in the water rich fissure area is revealed, and the water inflow mechanism of the tunnel in the water rich fissure area is discussed. The research shows that the maximum error between the theoretical calculated value and the field measured value is 8.1%, which verifies the rationality of the model and the correctness of the formula derivation. The water inflow of the tunnel increases with the increase of the maximum width of the crack, which is approximately linear due to the joint restriction of the water shutoff structure. When the ratio of grouting area thickness to tunnel radius is less than 2 times, the tunnel water inflow is significantly affected by the thickness of grouting area. The water inflow of tunnel in water rich fracture area is restricted by the fracture distribution law and support structure, so we should pay attention to the investigation of fracture distribution.