In order to calculate ammunition demand and understand the law of ammunition consumption, the system dynamic (SD) model was used to analyze the law of ammunition consumption for cross-shore firepower support. According to the basic idea of system dynamics, the SD model of ammunition consumption for cross-shore firepower support is constructed, and the causality of the model is analyzed. The SD flow chart of ammunition consumption for the engagement model is obtained, which is verified by simulation with typical cases. The simulation results show that the SD model can reflect the general trend of ammunition consumption in cross-shore fire support operations, and provide a reference for commanders to control the essential law of ammunition consumption from the macro level.