Abstract: A Time Window based Unmanned Aerial Vehicle (UAV) task Coalition Formation algorithm (TWCF) is proposed to solve effectively the problem of task assignment under the scenario of multiple targets and UAVs. The main idea of TWCF is to use the free time window for high effective and real time UAV task assignment. At first, the algorithm uses congestion avoidance mechanism to avoid the resource deadlock of real time task assignment. Then, a two stage coalition member selection algorithm is proposed to prosecute emergency tasks. Moreover, the algorithm can keep the computation overhead effectively to fit the real time and low complex requirement of battlefield. The simulation results show that TWCF increases effectively the completion ratio and reduces the task completion time while the computation overhead keeps at low level all the time.