Abstract: The algorithm of state estimator for maneuvering target is studied based on the assumption of quasi-steady state of flight path of the fighter. By selecting virtual measure variable and state variable, and by supposing the flight path of target is in quasi-steady state, this algorithm converts the problem ofnonlinear filtering and estimation with nine variables into one three-ordered and three two-ordered linear filtering and estimation problems. It is showed that the algorithm has light computing load and good filter precision, and is capacity to meet the requirements of integrated control in the simulation result of integrated control system.