In this letter, discrete complex image method is employed to compute the Green’s functions in the spatial domain, which improves the speed of evaluating the impedance matrix. The triangle vector basis function-RWG, is used to simulate the current distribution in order to compute the scattering properties of arbitrary shape microstrip patch without the staircase approximation. The numerical result shows the validity of the proposed method. In this letter, discrete complex image method is employed to compute the Green’s functions in the spatial domain, which improves the speed of evaluating the impedance matrix. The triangle vector basis function-RWG, is used to simulate the current distribution in order to compute the scattering properties of arbitrary shape microstrip patch without the staircase approximation. The numerical result shows the validity of the proposed method.