Aiming at the problem that tethered unmanned aerial vehicle (UAV) can not be located under the condition of navigation satellite denial, a vision positioning system based on cooperative target is designed. By constructing the vision positioning system, the target detection algorithm, the target offset calculation algorithm and the data smoothing algorithm are designed to realize the passive positioning of the tethered UAV. The test results show that the UAV can accurately detect the ground target and calculate the relative position in the process of flight, take-off and landing, which can effectively solve the positioning problem without satellite signals.