This paper is for the identification of the RCS sequence of the mid-course missile. On the basis of analyzing its motion and electromagnetic scattering characteristic, a new method using RCS magnitude changes with respect to the object gesture angle for inversing the mid-course object's two-dimensional length was presented. Compared with the traditional ellipse method, the new method overcomes the disadvantage of the necessity for the maximal and minimal RCS value of the object. The experiment results tested by the simulated and darkroom measurement of the representative missile object show the effectiveness of the method.