The difference in structure parameters can be utilized to distinguish different space cone targets effectively. Due to the fact that the high resolution range profile (HRRP) sequence contains the structure and shape information of the observed target, an inversion method for geometrical structure parameters of space cone targets based on the HRRP sequence was proposed in this paper. Firstly, the projected length of the target under different radar line of sight conditions was analyzed. Then, aiming at the problem of a relatively large error of the projected length extracted by the traditional threshold method under the strong noise condition in the actual measurement, a method to estimate the projected length was proposed after extraction of the optimum path by the improved ant colony algorithm. Finally, the generatrix length and the half cone angle were estimated by the triangular fitting. By comparison of the traditional method through simulation, it was demonstrated that the proposed method could still obtain relatively high estimation accuracy of structure parameters under the condition of a comparatively low signal-to-noise ratio.