High power fiber-coupled diode lasers are widely applied in laser material processing. Based on the commercial diode laser stacks, a comprehensive study of fiber-coupled diode lasers was presented using visualized beam shaping simulations. And then in experiment, refraction optical beam shaping, polarization multiplexing, wavelength multiplexing, and fiber coupling were used to produce a 4.08 kW output from an optical fiber with core diameter of 800 μm and NA of 0.2. An average fiber coupling efficiency about 95% was obtained, which was in good agreement with the simulation.