In order to research the effects of laser power,scan velocity and beam diameter on the primary and secondary degree that affect the 38CrMoAlA steel′s laser phase transformation hardening,and optimize the technical parameters,the normal experiment was conducted by three factors and three level L9(33) normal experiment table. The effect of laser power,scan velocity on the surface hardness was predicted on the basis of two dimension bicubic interpolatio. Results show that the primary and secondary sequence affecting surface hardness is scan velocity,laser power and beam diameter,and their optimized level are 30 mm/s,1.6 kW and 3.5 mm respectively. Under the three parameters,the hardened depth of laser phase transformation can reach over 0.5 mm. The hardened layer can be divided into four parts. Almost all of the second layer is martensite and this layer has the highest hardness. The structure coarsening happened to the fouth layer,which is the mixture of martensite and ferrite and has the lowest hardness.