The microstructure, corrosion and corrosion fatigue properties of 40# Cr steel irradiated with a 2kW CO2 laser beam have been studied using optical and scanning electronic microscopy. Experimental results show that the increase of corrosion resistance of materials depends on the laser irradiation parameters. The corrosion resistance of specimens treated with laser transformation hardening is better than that of the specimen treated with laser melting-resolidification, and the corrosion fatigue life time of the specimens irradiated with laser is 2.58~6.94 times that of the unirradiated ones, and the corrosion resistance mechanism, the characteristics and mechanism of the corrosion fatigue of the materials are analysed.