Abstract: Due to the sudden shutdown of pump, the power off or the mechanical failure, the flow velocity in the lifting pipeline of a deep-sea mining system may be changed in short time, which can be accompanied with a sharp pressure change. This phenomenon, the water hammer, may cause a great damage to the mining system. Based on the principles of continuity and momentum theorems of solid-liquid two-phase flow, a formula of water hammer pressure is derived for the lifting pipeline with coarse solid. By using the parameters of the pilot system, the water hammer pressure is calculated and analyzed under the conditions of different flow velocities, solid volume concentrations and pipe diameters. The results show that the parameters are important factors to the water hammer pressure, including the flow velocity, the solid volume concentration and the pipe diameter, especially, for the flow velocity. The results can provide some references for deep-sea mining system designs and safety risk analysis.