In this paper, we present a phase-interface-based heat source model and analyze the temperature and flow fields of a 3 mm steel plate during laser perforation based on the thermal fluid-solid coupling effect. The model truly reflects the dynamic process of temperature and flow fields, and the calculation results can effectively explain the influence of laser heat source and auxiliary gas on laser perforation. The simulation results show that, in the early stage of laser perforation, under the influence of auxiliary gas and heat source, the keyhole has a stronger blowing ability, fewer deposits on both sides, and slightly vibrates in the horizontal direction. With the increase in keyhole depth, the keyhole shape tends to be stable, the keyhole center is reduced under gas thermal convection, and the auxiliary gas' blowing ability is weakened, increasing the amount of molten matter at the bottom of the keyhole. The confirmatory experiment results show that the amount of molten matter increases with an increase in the hole depth, which is consistent with the simulation results. The phase interface-based heat source model can simulate the interaction between the temperature and flow fields in laser perforation efficiently and can reflect heat accumulation during laser perforation. It provides a theoretical basis for laser perforation.