Conventional plain gates cannot be used to block or store water due to the risk of gate failure at water intakes, such as diversion tunnels, ecological tunnels, and water galleries of dams. A physical model test was conducted to examine the impact force of the gate under different water levels. Three different blocking structures were re-examined: plain gate, multi-blocking gate, and disc-blocking gate. The equation of motion for the blocking gate under a constant water head series was established. The falling motion was described more accurately, and the theoretical impact force was obtained by using the impulse theorem. The results indicated that the experimental and theoretical results were consistent basically. It is recommended to consider various indexes and engineering operability when reducing the water level of the reservoir and blocking the gate. The proposed theoretical formula and implementation method can serve as a theoretical and practical basis for emergency blocking.