Abstract: Wing and pylon form a structure which is the major lateral scattering sources of an ordinary aircraft because a dihedral angle of ninety degrees is formed. In order to implement a reduction of RCS without any other change on the aircraft, the outline of the pylon is changed by applying a serrated scheme and the right dihedral angle structure is removed, so coupling effect is waken. Computation results reveal that the RCS of the wing-pylon structure on a domestic active fighter plane is reduced by 9 to 13 dBsm in the typical lateral attitude angle range. So it is proved that the serrated scheme could be significant useful in the control of the lateral coupling RCS of the ordinary aircraft. The ray trace method is used to do the calculation of the RCS.