Abstract: This papar extended the optimal constant gain filter considered by K. C.Wilson to the case involving radius velocity measurements. With a maneuvering target, the maneuver detector, the estimation of velocity input incremeuts and the updating of state predications are discussed. Comparing this filter with the Kalman-filter and constant gain filter,computer simulation results show that the filter deviation in tracking a maneuvering target is reduced, the filter precision in maneuver range improved, while the fine tracking characteristics of the Kalman filters to non-maneuvering targets is retained.