A method of analysing and calculating the Radar Cross Section（RCS） for Complex aircraft targets is presented and verified.The method utilizes a computer program for modeling targets’geometry in terms of surface fitting.The actual exterior surface can be accurately modeled with spline function and divided into a lot of small surface elements. The scattering field calculation is based on the Physical Optics approximation for standard surface sheet.The total scartering field of the target can be obtained by using phase synthesis.The modeling procedure and some examples are given to verify the validrty of the method and presentation is limited to monostatic case for perfectly conduction targets.