High efficiency coupling between free-space laser and optical fiber c an reduce loss of the laser energy greatly.The characteristics of laser after single lens transformation are analy zed,on the basis of propagation law of Gauss beam passing through lens.Focal length parameters of the lens are selecte d to match well between laser and the optical fiber parameters.For a certain laser wavelength,the smaller thefocal length of matching lens,the smaller thelaser waist spot,but the larger the num erical aperture NA is.Therefore,it is necessary to consider the parameters of th e focal length and the numerical aperture of the focusing lens,so as to meet the high-efficiency coupling of space laser and single-mode fiber. The waist size of laser propagating to the end sur face of optical fiber r is less than 10micron meter and the numerical aperture is less than 0.12.Thus the free-space l aser can be coupled into single mode fiber with a high efficiency.An application case is given to illustrate the pro posed approach.780nm laser in free space coupled into a single mode fiber is analyzed and a single lens with focal length of 5mm is used.The results show that coupling efficiency is as high as 90%.The coupling system has simple structure and high transmission efficiency from free space to optical fiber.This study has certain reference si gnificance for analyzing the efficient coupling between free-space laser and op tical fibers.