Abstract: The stress distribution and evolving surface settlement during tunneling and excavating surrounding rockmass after grouting were studied with FLAC3D for the change in the mechanic properties of grouted surrounding rockmass. The simulation results in contrast to engineering practice indicated that the grouting serves the function of shielding to reinforce tunneling and both sides of reinforced rockmass are the stress concentration area. With the 3/4 part(270°) of a circular hole used for grouting, the settling amount due to excavation in simulation is minimum, i.e. 22.3mm which becomes 27.1mm in practical monitoring. Therefore, it is feasible to forecast the reinforcement effect by simulation with FLAC^3D. The reason why the simulated settling amount deviates from that monitored relates to the idealized grouting construction. It's of importance to increasing the grouting pressure gradually and to judging whether the grouting process should be ended according to both the finishing pressure and grouting amount so as to ensure the grouting quality.