Abstract: In the grouting reinforcement project, in order to avoid the instability of the support structure due to excessive force caused by spatial variability, a reasonable prediction method for the stiffness and strength of grouting reinforced body is necessary. The fractal theory is used to describe the pore characteristics of the granular soil type tunnel surrounding rock, and the conversion relationship between the body porosity and surface porosity of the surrounding rock is established based on the empirical formula of tortuosity. A new macroscopic stiffness prediction method for grouting reinforced body is proposed based on the Mori-Tanaka method with the body porosity as the variable. By using energy method to solve the bulking critical load of different half-wave distribution patterns of connecting pores as the uniaxial compressive strength of the grouting reinforced body, so that a new theoretical model for strength prediction of grouted reinforced body is established. The Yujingshan tunnel is used as the engineering background, the method proposed by this paper is secondly developed in FLAC^3D, by randomly generating porosity for different surrounding rock elements, the mechanical properties calculated by proposed stiffness and strength prediction methods of grouting reinforced body is assigned to the surrounding rock elements, and the spatial variability of surrounding rock is realized. The maximum absolute error of the horizontal convergence of the tunnel between simulation and monitoring result is only 8 mm. The numerical simulation results show that the grouting reinforcement of the backfill region of Yujingshan tunnel can reduce the surrounding rock displacement by 50%-90%, greatly reduce the bending moment of support structure corresponding to surrounding rock region which has poorly physical and mechanical properties, reduce the support structure torque to 0, and control the support deformation within 10 mm. However, the load distribution law between the backfill region and limestone cannot be changed by grouting.