The absorption rate of red copper to fiber laser with wavelength was low, only was 4%, required of high power laser to weld, high power was easy to produce defects such as pores. In this paper, the blue light diode and fiber laser were used to weld the red copper with a thickness of 3 mm, and the welding process parameters were optimized. The cross section and micro-structure of fiber laser welding, blue light diode laser welding, blue light diode laser and fiber laser composite welding were compared and analyzed, and the micro hardness of the welds was tested. When the diode laser was 1 000 W, the fiber laser was 2 000 W, and the welding speed was 10 mm/s, the 3 mm copper can be welded, and the tensile strength of the weld reached to 182 MPa, which was 60% of the tensile strength of the base metal, and there was no porosity in the welds. The composite optical fiber laser welding and blue diode laser welding, used the high absorption rate of copper in wavelength of 450 nm, the total input power was low, which can maintain the stability of the molten pool, and can improve the fluidity of molten pool. No pores would be generated, and the 3 mm thick was penetration welding.