Abstract: An algorithm of determining relative attitude and position between target and chase vehicles by quaternion estimation via ranges of feature points was interpreted,especially a new algorithm of solving for the ranges is presented.Also an error-transmission method was given to obtain the relative state errors from the image coordinate deviations directly,which can be used for evaluating the algorithm of determining relative state.Computational simulation results show that the precision of the algorithm provided almost reaches the theoretic values given by the error-transmission method.As to patterns of feature points,non-planar patterns(with 3 to 5 feature points) are better than co-planar patterns(with 4 feature points at least),and feature points in the base-plane should be distributed symmetrically.Among four-point co-planar patterns,square patterns are better than others.