Abstract: The experiment that 18Cr2Ni4W steels were treated by carburizing and laser transformation hardening was carried out. The microst ructure of the treated steel was studied in detail by SEM,TEM and image analyzer. The results show that the microstructure obviously varies with the change of depth in laser hardened zone;the large amount of residual austenite is produced due to existence of ally elements in the steel during laser transformation hardening,which decrease surface hardness;with the scanning speed going up,the hardness is increased.