Abstract: Based on diffraction theory, this paper deduces the equation of coherent beam intensity in far-field of with multi-core double-clad fiber. The effects of different fiber core arrays, especially single ring array, multilayer rings array, rectangular array and hexagon array, on the final quality of beam combination are investigated. The effects of different parameters including core diameter, core space, the distance between output plane and diffraction plane and wavelength are also studied. Numerical results demonstrate that, for given core number, single ring array is the best scheme among the above four core array in order to realize high quality beam combination, and the next one is rectangular array. Increasing core number can increase cross section utilization ratio，thus producing hig