Abstract ─ A fast and accurate method is derived and simulated to compute the mutual coherence function (MCF) of an electromagnetic beam wave propagating through atmospheric turbulence over a large interval of structure constant. This method is based on expanding the integral equation solution for one value of structure constant into its Pade’ approximation to cover large fluctuation interval. The expansion is compared with numerical results, and a very good agreement was obtained. Such computations are important in practical fields as remote sensing, imaging systems, and optical communications.