Abstract: Based on the modified Kirchhoff approximation, a modified geometrical highlight model of echoes from nonrigid surface sonar target with four parameters, including the amplitude, the time delay, the phase jump and the local plane wave reflection coefficient, is presented in this paper. The target strengths of rigid, naked and water filled,and silent tiles coated truncated elliptic cone shell are calculated using the former and the modified geometrical highlight models. The results show that the former geometrical highlight model with three parameters is approximation of one order for naked shells at high frequencies. For the actual shells, the modified geometrical highlight model with four parameters should be used whether it is coated or not with silent tiles.