This paper introduced a whole set of high-power СОr laser welding equipment with high beam quality, analyzed the optical system primarily, including the five-fold resonator of laser, three workspace light switched system, reflect focused system. The output power of the laser reached 2.5 kW and the output power fluctuation is ±4%。The ТЕМ00+ТЕМ01 laser beam with 1.6 mrad divergent angle has been obtained by the design of five-folded resonator, The ability of laser has been used properly and the efficiency has been improved by the use of three-workspace switch. The metal paraboloid reflector has been used to focus the beam in order to overcome the influence of thermal lens and spherical difference. Meanwhile, the 20CrMnTi alloy gears in automobile, gear-box have been welded, the welded seam with good appearance was obtained, the depth/width of the welded seam exceed 3:1, the thermal influenced zone is narrow and the melted zone has no shortcoming.