The Ni-P-nano-Al2O3 composite coatings were prepared onto medium carbon steel substrates by electroless plating method. The transverse-flow CO2 laser was employed for the heat treatment of the coatings at various scan velocities and power densities. The composition, microstructure, morphology, adhesion to the substrate and wear resistance of the coatings were characterized by energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), scratch test and friction and wear test (ball-on-disk). The effects of process parameters on microstructure and wear resistance of the coatings were investigated. It is found that the laser heat treatment conduces the microstructure from amorphous to crystalline structure, which comprises Ni3P and Ni phase, and Al2O3 phase remaines amorphous; the hardness of the coatings increases obviously for the phase transformation hardening. The friction coefficient increases due to the transformation of phase structure and the raise of surface roughness of the coatings, and the adhesion to the substrate decreases slightly. The main operating wear mechanism is abrasion. By treating with scan velocity 1.5～3.0 m/min, power density 5.0～8.3 kW/cm2, the coatings show high hardness, good wear resistance and a minimum wear rate of 1.21×10-5 mm3/(N·m).