Collapse may occur to if water inflow occurs during tunneling. In such case, the excavation should be stopped and the geological conditions and rock mass deformation in the waterinflow section should be predicted. Water inflow occurs near the exit of the right tube of Dakuishan tunnel. Ground penetrating radar (GPR) is used to predict the geological conditions of the waterinflow tunnel section. Analysis is made on the predicted geological conditions and the measured deformation data. The geological prediction results show that there is a confined water aquifer 2.5m below the tunnel floor and there is a huge cavity behind the tunnel lining. The deformation monitoring results show that the rock mass deformation exceeds 50 mm, which is higher than the limit value specified in relevant standards. Countermeasures, including concrete backfilling, advance grouting and steel rib installing, are taken on basis of the prediction results. In the end, the deformation of the tunnel section with waterinflow is brought into effective control.