An anti-rendezvous evasion maneuver method is proposed in order to escape from the spacecraft that has autonomous approaching ability. Supposing that a two impulse C-W navigation strategy is used by the approaching spacecraft, first a bearing-only relative navigation model is built. Then, a definition of degree of observability based on state estimation error is proposed so as to quantify observability. By using the degree of observability conception, the evasion maneuver direction is chosen as its gradient, which guarantees that every unit impulse can reduce the system observability mostly. Finally, the numerical simulation is conducted with different maneuver impulse, and the result shows that the method proposed can attenuate the system observability obviously. The method offers a new viewpoint for evasion maneuver research.