Cobalt-based laser cladding layer was prepared on the surface of 45 steel, and the microstructure of the cladding layer, the morphology of the molten pool and the wear resistance of the cladding layer were characterized by metallographic microscope (OM), scanning electron microscope (SEM), X-ray energy spectrometer (EDS) and friction and wear testing machine. Results show that the quality of the cladding layer increases first and then decreases with the increase of the laser power. When the laser power reaches 2 000 W, the quality of the cladding layer is the best, the molten pool is relatively stable, and there are no defects such as pores. The microstructure of the cladding layer changes from coarse and dispersed columnar crystals to fine and uniform equiaxed crystals, and finally to coarse columnar crystals. In the friction and wear test, with the increase of laser power, the wear mechanism of the cladding layer changes from massive exfoliation to particle wear. The wear resistance of the cladding layer is the best, and the real-time friction coefficient is the most stable. The wear rate is only 1.3×10-4 mm3/(N·m) under laser power of 2 000 W.