To the issue of tracking the ground moving target by formation of Unmanned Aerial Vehicles (UAVs), this paper presents a new strategy for the formation control in dynamic environment by using virtual structure together with behavior-based control method, with the UAVs distributed uniformly on a spherical surface with the virtual or actual leader as the center. A controlling variable designed by Lyapunov vectors is used for guiding the UAV formation to track the ground target. The obstacles are transformed into elliptic potential fields, and the tangent vector leads the UAV to avoid the obstacle with smooth trajectories. After passing the obstacles, the formation can be reconfigured and continued to track the target. Simulation result verifies the effectiveness of the proposed approach.