Because conventional numerical methods fail to evaluate the effectiveness of grouted bolts in reinforcing the surrounding rockmass, a simple and effective equivalent numerical method, with combination of a formulation for the bolt supporting pressure induced by rockmass deformation, is proposed for this purpose. In this method, the maximum axial force of each bolt is first determined by numerically simulating the bolt-supporting tunnel excavation. The obtained maximum axial force is then used to calculate the equivalent force distributing along the rock bolt by using the formulation of the bolt supporting pressure. Finally, the excavation process without bolt supporting is simulated by applying the equivalent distributing force to the surrounding rockmass surface. This method is applied to calculate the excavation and support of the underground powerhouse at Jinping Ⅱ hydropower station and the diversion tunnel #4 (section 0+550 m) at Wudongde hydropower station. By comparing the calculation results with the field measured data, it is found that the proposed method can well address the effectiveness of grouted bolts in reinforcing the surrounding rock, and the simulation results can provide reference for tunnel construction and support design.