Abstract: According to the complexity and changeability of the tunnels construction in karst aeras, geological disasters such as water flush and mud rush often occur during construction of tunnels ， which bring much economic loss to construction ， mostly also bring surface water to exhaustion and pollute environment ， etc. At present ， the effective measure to prevent disaster occurrence is improving the accuracy of the geological prediction in karst tunnels and taking the corresponding preventive measures promptly. First, the primary content of geological prediction is summarized. Then, as for the water flush in the process of excavating Qipanshi ^#3 cross tunnel ， the characteristics and types of caves in front of the face are analyzed based on the geological investigation, the location and size of the caves in front of the face are speculated by TSP-203, GPR and horizontal geological drilling machine, and the caves in front of the face are excavated based on the results of geological prediction. The actual situation after excavation and the geological prediction results are compared, the consistent parts of them are summarized ， the reasons of the inconsistent parts are analyzed, and the existing problems are discussed. The purpose of the research is to improve the accuracy of the geological prediction and to reduce the investment and casualties of the project to the best extent in construction of karst tunnels.