The temperature distribution and variation of HT250 gray cast iron during laser remelted are analyzed by establishing a three-dimensional transient simulation model, and the influence of laser power on the temperature field of laser melting pool is discussed. The geometric characteristics and microstructure of laser remelting single channels are observed by metallographic microscope and scanning electron microscope, respectively. The microhardness of the channel's cross section is measured by the microhardness tester. The results show that the remelted zone is semi-arc. From the surface to the inside, the remelted zone, the heat affected zone and the base metal are in turn. With the increase of laser power, the peak temperature of laser molten pool increases, the depth increases, and width of melt track deepens. The calculated geometry of the laser melted pool is in good agreement with the actual measurement of the laser melted pool, which proves that the model is reliable and effective. In addition, the experimental results show that the main microstructure of the HT250 gray cast iron in the remelted zone is very small dendritic modified ledeburite. The average microhardness of the remelted zone is about 1000 HV, which is about 5 times higher than that of the substrate.