Beam quality parameter plays an important role in the optical fiber coupling for the high-power laser. For high-power laser, its laser beam is always multimode, so it is an effective method to use equivalent basic mode to replace multimode for calculating. The beam width of this equivalent basic mode is measured by including 98% of the beam energy, and this is an effective way to calculate the beam quality parameter. A high-efficiency coupling system was designed by using theory of optical fiber coupling for the high-power laser and the beam transform, and in the system numerical values of lens′ aperture and focus were optimized. Experiment proves that the coupling system has a high coupling efficiency. The efficiency is more than 94% when the input power is 2000 W, and the figure of the experiment on coupling efficiency was displayed and analyzed.