Abstract: In this paper, we adopt the physical optics (PO) method to obtain the high frequency scattered fields from electrically large scatterers. Because the PO integral is highly oscillatory, the conventional quadrature rules like Gauss quadrature rule is very time-consuming. Hence, we propose a numerical steepest descent path method (NSDP) to handle this problem. We use the Lagrange interpolation method to get the quadratic amplitude and phase functions. Then, we transform the highly oscillatory integrand into a smooth and rapidly decreasing function by distorting the integral paths. This method greatly reduce the computational workload than brute force method. The NSDP method could divide the PO integral into several critical points contributions like stationary phase points, resonance points and vertex points in physical insights. The numerical results demonstrate that this method has advantages of error-controllable and frequency-independent.