Abstract: With contrast of different kinds of pores characterization in cladding layers fabricated on the substrates of 45 steel and H50, the composition, distribution and influence factors were investigated, respectively. The results show that the gas in pore was CO which was generated by the reaction of graphite and oxide. The shape of pores was irregular with many wedge angles. Furthermore, the floating path of pores was disperse instead of vertical due to the severe convection in molten pool. And the spread acceleration of pores was increased with the temperature as well as the surface tension gradient in the molten pool. However, the laser cladding parameters were the external factors affecting the distribution of pores. Enhancing the preheat temperature and reducing the laser power and laser scanning speed appropriately could avoid the generation of pores and decrease the porosity in the cladding layer.