Spot array laser alloying of C-Si-B-RE on nodular cast iron using CO2 laser has been made. The microstructure and characteristics of the alloying layer and HAZ have been analyzed and thermal fatigue tests on the laser treated samples have been done. The results demonstrate that laser alloying of C-Si-B-RE on nodular cast iron is able to achieve satisfying layers with high hardness and smooth surface which are free of cracks. The laser treated specimens were tested under the specified thermo-cyclic condition: 700 ℃～25 ℃, heating 90 s, cooling 10 s, 90 times. The results show that the initiation of the crack in the substrate is relevant to graphite nodular and its morphology. The thermal fatigue cracks in substrate and alloying area are retarded by the HAZ. The initiation of the crack in the HAZ is relevant to the oxide formed during thermal fatigue test. The refining pearlite colonies in heat affected zone (HAZ) compel the crack to develop slowly along the grain boundaries.