A silo discharge tunnel of someone hydropower station was simulated by FLUENT from reservoir upstream to its outlet downstream. The capacity of flood discharge, velocity, pressure were obtained, and were identical with that of the experiments. The simulation indicated that, complicated l flow of silo discharge tunnel with whirling currents can be simulated successfully by the combination of the k-ε double equations turbulent model, VOF method, structured and unstructured grid. The simulation supplies a new method for the study on the silo discharge tunnel with whirling currents.