In this paper, Cr12 steel was taken as the research object, and laser micro melting model was established in comsol software based on physical equations such as laser heat source, convection heat transfer, evaporation mobility, recoil pressure, Marangoni effect. The forming mechanism and evolution law of concave–convex microtexture morphology were studied by numerical simulation. The research reveals the changing process of the velocity of the flow field inside the material during the surface deformation. In addition, it can be found from the temperature field changes under different power that the higher the power is, the faster the surface temperature of Cr12 material increases in the process of thermal deformation. And the hardness of the microtexture was greatly improved after the material experienced sudden heat and cold in a very short time. By comparing the numerical simulation results and the experimental results, it can be found that with the increase of power, the height, depth and diameter of the concave–convex microtexture morphology all show an increasing trend, and the surface geometry obtained through numerical simulation matches well with the experimental results. It indicates that the numerical simulation has high feasibility and can effectively reflect the forming process and morphology of concave-convex microtexture.