Laser cladding experiment of nickel base alloy and cobalt base alloy on the Q235 steel was done with a 3 kW transversely flow CO2 laser. It was discovered that suitable rare-earth oxide additives promoted size of crystallites in the cladding layer to coarsen obviously, and thermal shock resistance of the layer rose by over 10 times, which is quite important to the application and study of laser cladding technology at high temperature or thermal shock situation. Mechanisms about effect of on the laser cladding layer were discussed in this paper.