Abstract: A double-clad fiber collimator applied in high-power lasers was proposed. Considering the 8wedge angle of C-lens and the tail of double-clad fiber in the process of production, at the same time to consider the coupling efficiency with double-clad fiber tail, the transform matrix was modeled and calculated from the general model of Gaussian-beam through a complex optical system, using the theory of matrix optics in meridian plane and sagittal plane respectively. Combined with practical applications in double-clad fiber and C-lens related parameters, the influence of the distance between fiber tail and Clens and the influence of the parameters of the C-lens on working distance and beam waist diameter of collimator were both stimulated and analyzed. The results may be to direct the design of collimator in high-energy laser system.