Herein, the stress distribution state of laser phase transformation hardening vermicular graphite cast iron RuT300 is studied based on beam discretization using a constructed elastic-plastic constitutive model of the discrete laser phase transformation hardening RuT300. Additionally, the model considers the effect of temperature on thermal stress and residual stress. The results demonstrate that the large thermal stress on the material's surface corresponds to a two-dimensional discrete lattice spot. Since rapid laser heating causes each part of the material to experience a different temperature, the thermal stress distribution is wavy along the X-axis path of the model. The maximum thermal stress in the X and Y directions of the discrete spot loading region is found to be -635 MPa, which is 1.8 times that found in the Z direction. In each section of the model, the thermal stress decreases gradually with an increase in the depth; the residual stress value in the laser loading region on the surface of the material is larger than that in the nonloading region. The residual tensile stresses in the X and Y directions of the model constitute the primary residual stress, with a value of approximately 200 MPa. The residual stress in the X direction along the X-axis path is the largest among the three directions. As the laser power increases, the peak residual stress value increases, and the area of the material affected by large residual stresses increases. However, when the laser heating time is prolonged, the change in the peak residual stress value in the loading region is within the range of 2.4 MPa.