Fire water monitor is one of the most commonly used equipments in fire fighting. A liquamatic fire water monitor with self-swinging device was designed. The mechanism of an impeller driving four bar linkage was applied as the self-swinging device. The working principle of the liquamatic fire water monitor was introduced. The internal flow performance was simulated using Fluent software; and the influence rules on jet characteristics were analyzed by changing the cross-sectional shape and diameters of the monitor body, inlet pressure and drive set of the self-swinging device. These analyses led to the optimal structural parameters of flow channel. These simulation results will provide useful theoretical guidance for design of other types of fire water monitor.