The temperature field is studied and the process parameters are optimized for the laser cladding based on the internal wire feeding of three beams. A heat source model of the three beams is established. The temperature field of the molten pool is simulated by using the ANSYS software. The effects of defocusing amount, laser power, and scanning speed on the morphology of the cladding layer are analyzed by experiments and simulations. The simulation and experimental results demonstrate that the defocusing amount considerably impacts the width of the cladding layer and the morphology of the dilution zone. The laser power mainly affects the dilution rate of the cladding layer, and the scanning speed considerably impacts the height of the cladding layer. Further, the change of the scanning direction impacts the dilution area of the cladding layer. The experiments are performed under a defocusing amount of -2 mm, a laser power of 1500 W, and a scanning speed of 5 mm·s ^-1. The cladding layer is smooth and exhibits no obvious cladding defects. The cladding layer structure is martensite, the hardness is 411 HV, and the hardness distribution is relatively uniform.