Taking the water inflow cases as example, the authors analyze on the forming process of the underground karst rivers in the water inflow zones by means of geology method and applies the analysis results into the water inflow predictions; The authors analyze on the mechanisms of the karst water inflows and expatiate on the karst development conditions and the scope and contents of the construction geological investigations. The authors analyze on the causes for the water inflows/outbursts from several aspects and present the factors that should be considered in the determination of the thickness of the safe rock walls during construction. The authors also provide their recommended thickness of the safe rock walls of the project and recommend some construction countermeasures.