Infrared detector can only obtain the azimuth angle and elevation angle of the target which is hard to get the information of distance.Especially for the incomplete information measured by motional infrared detector,it is impossible to track three dimensional objects in rectangular coordinates.Aiming at this issue,a new approach,the algorithm of filtering and smoothing with parameters based on motional infrared mono-station,is proposed to estimate the direction of flight path,with the utilization of the information of azimuth angle and elevation angle measured by the sensors,and then the problem of target tracking by motional infrared mono-station is well solved.As is shown in the simulation,the model has a good estimation of the course of the target as well as the direction from the missile to targets.The algorithm has high value of theory and application.