Abstract: In order to study the influence of laser power on the surface modified layer of H13 steel after laser quenching and prepare the laser quenched modified layer under the optimal process parameters, the temperature evolution law of the quenching process of H13 steel was simulated by COMSOL, the depth of hardened layer was predicted, and the laser quenching experiment was carried out. The macroscopic morphology, microstructure evolution mechanism, elements and microhardness of H13 steel after laser quenching were analyzed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and microhardness tester. The results show that the depth of hardened layer predicted by simulation is basically consistent with the experimental results. The microstructure in the depth direction of the laser scanning area is refined obviously, and the hardness is gradient distribution. From the quenching surface to the inside, it is divided into phase transformation hardening zone, transition zone and matrix. The microstructure of phase transformation hardening zone evolves from original pearlite and ferrite to fine needle or lath martensite. When the laser process parameters are not selected properly, the phenomenon of overburning melting will be caused, which will affect the surface smoothness of the workpiece. When the laser power is 600 W and the scanning speed is 10 mm/s, the depth of the hardened layer can reach 0.41 mm, and the highest microhardness is 709.6 HV_0.3, which is about 3 times of the matrix.