After convertmg the measurements of detector , such as radar , in ball-coordinate system to the measurements m tnangular rectangular-coordinates system , the error distribution ruler will be changed. By analysis the theoretical model is showed not to be suited for Kalman filtermg directly , the engmeenng model is obtained to be suited for Kalman filtenng and then the theoretlcal model is numerically compared with the engmeermg model on ltS numerical characteristics. They are m close proximity.