In the process of ammunition support， the amount of ammunition reserve in wartime affects not only a certain aspect of the ammunition support system but the whole system. The traditional experience alone cannot make a correct judgment on some decisions. This model proposes a method based on system dynamics， analyzes the internal factors of the ammunition supply system in wartime， and establishes the dynamics model of the ammunition support system in wartime. Under the condition that ammunition consumption rate and ammunition supply time are fixed， the optimal value of unit ammunition reserve is calculated by vensim software simulation. The influence of ammunition replenishment time and ammunition reserve before the war on ammunition support during wartime is analyzed by changing the ammunition replenishment time and ammunition reserve before war combined with the fluctuation curve of ammunition replenishment rate， to obtain the numerical influence of the change of one variable on other variables， which can provide relevant data reference for commanders in ammunition support decision-making.