By analysing the uplift pressures of dam foundation, water quality, and pH values before and after the construction of the Chencun Dam, the changes of seepage characteristics are discussed. The tendency of permeability coefficient is forecasted by use of ARIMA model. The movement of seepage and change of water quality will influence the dam security. The observed data after the power station operation show that the seepage field is changed obvioussly, groundwater level is degraded, and the uplift pressures are widespreadly reduced, but the pressure exerted by reservoir water on the curtain and soft rock is raised. The alkalinity in water is beneficial to protect the concrete of the dam from corrosion. It is seen from comparison the forecasted values given by the model are in good agreement with the monitored data.