A dynamic task assignment algorithm based on local exchange mechanism is proposed to meet the real-time, the single performance of a single UAV cluster and the constraints of task resources requirement of task assignment in dynamic environment, Based on the conflict-free assignment scheme that has been formed in the initial stage, the UAV cluster performs the tasks according to the task sequence that each needs to perform, In this process, in the face of the newly discovered targets, it is not necessary to carry out global redistribution, but to make use of the past solving history and judge on the basis of the original execution task sequence that if the exchange conditions in the contract network are met, local exchange will be carried out to obtain the relatively highest task income to adapt to the changes of UAV cluster strike resources and environment greatly improves the efficiency of task allocation.