To strengthen the surface performance of medium steel,Ni-P-Al₂O₃ electroless composite plating was produced on 45# steel,and then treated by pulsed Nd:YAG laser beam. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure of the coating. X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were employed to analyze the phases and elements of the coating. The micro-hardness of pulse laser processing was tested. The results reveal that the hardened coating has good performance with uniform components and fined microstructure. The phases in hardened layer obviously change,the coating is divided into five regions from the surface to inner as follows:dendrite region,cystiform crystal zone,columnar crystal zone,fusion zone,heat affected zone (HAZ) and substrate. After laser process,the coating obviously transits from amorphous state to crystalline state,where non-equilibrium phases such as Al5FeNi,FeNi and Fe0.64Ni0.36 were found. The microhardness of hardened region is about 1.7 times of as-deposited layer and 4.5 times of the substrate owing to dispersion and transformation strengthening.