Being not considerated the influence of spherical aberration,the coupling efficiency of fiber-output laser computed by Gaussian beam lens formula is higher.In this paper,the ray-tracing method is used to analyze the Gaussian beam lens trannspositional process.Firstly,to abtain the parameters of coupling system,such as the focal length and the position of the lens,computing the Gaussian lens formula,then establishing the rectangular coordinate system and constructing equation and tracing the marginal ray to compute the parameter of the radius of the image beam waist.Calculating the coupling efficiency between fiber and beam by different waist beam which computed by different method,then comparing.The result indicates that the spherical aberration of positive lens reduce the coupling efficiency.At last,the coupling efficiency is improved by using doublets rathar than single lens.