According to the diameter of the molten pool on the surface of the metal substrate after laser derusting, the tem-perature field distribution of the metal substrate surface is characterized by finite element simulation. The pulsed laser used in laser descaling had the characteristics of small laser power, large repetition frequency, short pulse width and high metal reflectance. Therefore, Gaussian surface heat source and finite element meshing strategy could be used to describe temperature field distribution on the surface of the metal substrate during laser derusting. The size of the molten pool on the surface of the metal substrate after laser derusting was measured and observed by a white light interferometer and a scanning electron microscope. After repeated simulation calculations and comparison of experimental results, the parameters of the Gaussian surface heat source were determined as follows: heat source efficiency of 48%, gaussian coefficient of 1 and heat source radius of 30 mm. According to the relationship between temperature and time of a single node on the surface of the metal substrate, a very rapid heating and cooling temperature field was formed on the surface of the metal substrate during the laser derusting process. According to the diameter of the molten pool on the surface of the metal substrate after laser derusting, the parameters of the pyrogen model are determined, and the more accurate distribution of the temperature field on the surface of the metal substrate is obtained by simulation calculations.