Fire water monitor is an important instrument for the largescale firefighting, and it is changing toward large flow, long jet range, high jet altitude, and so on. The nozzle is one of the core components of the fire water monitor, and its design directly influences the jet performance. The flow field numerical simulation on the fire water monitor nozzles with three different inner contours was carried out by Fluent, and the effects of contours on the jet pressure, velocity and turbulent kinetic energy were analyzed to determine the optimal inner contour of the fire water monitor nozzle. It can be seen from the experimental results that at the flow rates of 40, 50, 60 and 80 L/s, the nozzle with the sinusoidal inner contour curve generally has higher jet range than the national standard by more than 15%. The above research provides reference for improving the jet performance of the fire water monitor.