In view of the fast speed and strong maneuverability of offshore threat targets and in order to improve the quality and speed of solving the problem of USV formation′s firepower allocation in coastal defense,a multi-constraint dynamic firepower allocation model of USV formation in line with the actual battlefield is established,and the improved ant colony algorithm is used to solve the model.The model not only considers the dynamic motion of threat targets and multi-facet resource constraints comprehensively,but also places higher demands on the search ability of the algorithm.The improved algorithm can avoid falling into local optimum on the basis of satisfying the global search by adjusting the update mode of the pheromone and adopting the time-varying volatile factor.The result of Monte Carlo simulation shows that：Compared with the traditional ant colony algorithm,the improved algorithm can greatly improve the effectiveness, convergence and real-time performance of solving the USV formation′s firepower allocation problem in coastal defense,and has certain application value.