A complete analytical method for coefficient of charge on plane elements in SCM(surface charge method) is complicated under linear or high order charge density approximation.A kind of semi-analytical integration is proposed.It transforms the integral under local reference into a separable double integration under global reference.Since the inner layer integration is analytical,the original integration can be simplified to a one-dimensional problem which can be calculated by traditional numerical method.As for singular integral,eliminating singularity technique by adding auxiliary function is adopted.It indicates that high precision is achieved and the method is applicable.