According to the geological situation of Lijiachong tunnel, the paper studied the grouting effect of tunnel with soft and weak surrounding rock by use of FLAC3Dsoftware, analyzed the change of plastic zones of surrounding rock before and after grouting and the change of deep displacements with time during the construction of tunnel. The results indicated that pre-grouting can narrow the range of plastic zone, improve the physical and mechanical properties of surrounding rock and also effectively control the deep displacements of surrounding rock.The difference of the results gotten by numerical analysis and practical monitoring is not great. The FLAC3D software can be used to study the grouting effect of surrounding rock.