Ni-based spontaneous melting alloy powder and Co - based spontaneous melting alloy powder are selected for laser cladding on the mild steel substrate with the fore-put powder and the coaxial powder feeding respectively. Laser power is 2. 0 kW, laser beam spot diameter 2. 0 mm,scanning speed 0. 15-0. 25 m/min. The results show that the microstructure of the coaxial powder feeding laser cladding layer is finer than that of the fore-put powder laser cladding layer (the former 2. 5-4. 0 μm, the latter 5. 0-10. 0 μm) .and thermal shock resistance of the former is better than that of the latter. Obviously, this is very significant because the coaxial powder feeding laser cladding is easy to realize automation and big area cladding.