Target allocating plays an important role in command and control system. In order to adapt to the multi-scene situation, the target assignment algorithm in the swarm USVs is studied in the paper to carry out the joint attack tactics against the enemy, and it needs to formulate the optimal operation plan according to the actual composition of the enemy and our resources. The target assignment algorithm proposed in the paper arranges the best attack target for each individual, so as to maximize the cooperative attack efficiency of the swarm to achieve the best simulation effect. The real results show that the method can provide the optimal task allocation for the USV swarm, so that it is one of means for auxiliary decision making.