Abstract: For explicitly understanding the thermo-mechanism of laser melting process on cast iron, a validated dynamic three-dimensional numerical modal for this process was established by taking into account the thermal physical parameters and latent heat of the material. The temperature field and the relationships between different process parameters were studied with this model, and the simulation results were in accordance with the experimental results. The results indicate that the penetration depth of the laser melting process on cast iron is grater than that on the steel. The large temperature gradients inside and outside the molten pool are dominated by the depth and width components respectively. A larger temperature gradient is gained through reducing scan speed and spot size. The pool is shrunk by the increase of scan speed and spot radius; the solidification speed is raised with the increase of laser scan speed and reduction of the spot size.