The aeroengine is a main contribution to the backward electromagnetic scattering of the aircraft, and the radar cross section(RCS) reduction measures adopted enable to effectively improve the aircraft stealth performance. The spherical convergent flap nozzle (SCFN)can meet the comprehensive needs of new generation fighters for maneuverability and stealth. The iterative physical optics method is used to calculate the backward RCS of the spherical convergence vector nozzle under different angles of beveling and tooth modification. The results show that the beveling modification has a better RCS reduction ability at the pitch plane. When the beveling is at an angle of 30°, the reduction ability is better than that of the other beveling angle. The tooth modification has RCS reductionability at the both plane. When the tooth angle is at an angle of 100°, the reduction ability is better than that of the other tooth angle. The shape modification of aero engines requires comprehensive consideration in the aircraft design stage.