Sense and Avoid (SAA) has been identified as one of the most significant challenge for integrating UAV into civil airspace, and vision system has demonstrated its capacity to SAA.To deal with the depth-independent vision based sense and avoid problem, an image-based envelop formulation method is proposed and single point feature is found.Then aangle only visual servoing controller is designed to track the selected point at the same time the motion of the feature point is compensated.In the end,simulationrepresent different collision scenarios are carried out to illustrate the feasibility of the proposed method, the simulation results demonstrate that the method in this article can achieve SAA in without range information.