In order to optimize design and establish a study foundation for outside flow-field, computational models for solving pressure, velocity of water column and friction force in the launch pipe of pulsed anti-riots water cannon are H55established. Commercial software FLUENT is used to simulate the process of high-pressure gas impinging into water column,k-εmodel is used to describe the turbulence distribution, and VOF model is used to trace the gas-liquid interface in pipe. Through the simulation, the gas-liquid interface evolvement image, vector distribution of exit velocity and pressure distribution at symmetrical axis in launch pipe are gained. The theoretical calculation values of the established models are compared with the simulation results, and the situation of their conforming with each other is analyzed. The move of water column is influenced by the inertia force primarily, not by the gravitation. The greater pressure grad presents in the water column area, the theoretical calculation value and the simulation result match well, and the latter one can be used to amend the computational model. The conclusion obtained has some guide sense in the study of outside flow-field, the design of water cannon or same non-lethal weapons.