Distributed task assignment algorithm is the key algorithm to solve multi-agent task assignment problem. In this paper, heterogeneous UAVs cooperative search and combat task is taken as the background. First, a multi-UAV task assignment model is established by comprehensively considering the constraints of UAV load resources, task time window and task type. Aiming at the obstacle threat in the task scenario, the UAV motion model is considered to improve the mobility and obstacle avoidance ability of the UAV in the assignment model. Second, UAV maneuver trajectory and path in the Consensus-Based Bundle Algorithm (CBBA) are improved by integrating dynamic window algorithm (DWA). Finally, the proposed algorithm is verfied which can improve the ability of multi-UAV task assignment in complex environment through numerical simulation.