Electromagnetic scattering characteristics of the microstrip antenna array is analyzed by using the adaptively modified characteristic basis function method (AMCBFM). Volume electric field integral equation and SWG basis function are applied to the material region, while the surface electric field integral equation and RWG basis function are applied on the conducting surface of the microstrip antenna array. The method of moments (MoM) is used to convert the integral equation into a matrix equation. The bistatic RCS of 7×7microstrip antenna array and the monostatic RCS of 2×2microstrip antenna array are analyzed numerically. The results indicate that the proposed method has a series of merits:reducing the size of the matrix equation into a small level and saving the memory requirments.