Abstract: Sediment deposition is a big problem that affects the lifespan of reservoirs in heavily sediment-laden rivers. Furthermore, venting turbidity currents is an important measure to reduce the sedimentation in reservoirs, especially at the initial operation stage of the Xiaolangdi Reservoir. The occurrence of plunge point means the formation of turbidity current, and the research into the prediction of turbidity current formation can help to better understand its motion laws in reservoirs. Qualitative descriptions and quantitative calculation methods for the prediction of turbidity current formation are summarized firstly in this paper, with the shortcomings and application conditions of these methods also being given. The momentum equation for the motion of turbidity current is then deduced, and the effects of non-uniform vertical distributions of sediment concentration and velocity on the formation of plunge point are investigated. Finally, a new formula for predicting the formation of turbidity currents is proposed herein, and its predictive accuracy is validated by lots of flume and field measurements. Validated results indicate that the proposed formula can be used to predict the formation of turbidity currents in the Xiaolangdi Reservoir.