Solving electromagnetic (EM) problems by integral equation methods relies on the accurate evaluation of singular integrals related to the Green\´s function. In the method of moments (MoM) with the Rao-Wilton-Glisson (RWG) basis function for solving surface integral equations (SIEs), the gradient operator on the scalar Green\´s function can be moved onto the basic function and testing function, resulting in a
weak singularity in the integral kernel, where
is the distance between an observation point and a source point. The weakly singular integral can be evaluated with the well-known Duffy\´s method, but it requires a two-fold numerical integration. In this work, we develop a novel approach to evaluate the singular integral by using a local polar coordinate system. The approach can automatically cancel the singularity and reduce the integral to a one-fold numerical integration by deriving a closed-form expression for the integral over the polar coordinate. Numerical examples are presented to demonstrate the effectiveness of the approach.