Grey situation commonly exists in target assignment of ship-based UAV formation in coordinated air-to-sea attacking due to limit of early-warning and detection level,incomplete information,and favor and bounded rationality of decision-makers.Aiming at the problem,the target assignment strategy set and payoff matrix of UAV formation and surface ship formation were established.Then,a model of target assignment of ship-based UAV formation for coordinated air-to-sea attacking was constructed based on grey bi-matrix game theory.An improved PSO algorithm was designed to solve the problem with reformed particle location updating formula.Simulations were carried out by using GA,traditional PSO and the improved PSO algorithm respectively.The results indicate that:1) The improved PSO algorithm can avoid local optimum solution and converge to the globally optimum solution;and 2) The grey bi-matrix game theory based target assignment model can well solve the grey problem in target assignment.The results prove the practicability of the model and the effectiveness of the algorithm.