To solve the problems of low energy coupling efficiency and poor process stability in laser welding of red copper, we use the method of adding auxiliary magnetic field to increase the absorption of laser energy by the welding base metal, and establish a numerical simulation model of magnetic field assisted laser welding of T2 red copper. The temperature field and velocity field of molten pool with and without magnetic field are compared and analyzed to explore the influence of magnetic field addition on the temperature distribution and fluid flow evolution of laser welding molten pool of red copper. The results show that with the addition of the magnetic field, the maximum temperature of the molten pool increases from 4476 K to 4868 K, an increase of about 8.7%. The average flow velocity of the molten pool decreases, and the maximum flow velocity decreases by about 21.97%. When the simulation time at 280 ms, the width and depth of the welding pool without additional magnetic field are 2.12 mm and 1.29 mm, respectively, and the width and depth of the welding pool with 120 mT intensity magnetic field are 2.26 mm and 1.34 mm, respectively. Finally, the simulated fusion line morphology is compared with the experimental fusion line morphology, and they have a high degree of fit, which verifies the accuracy of the established numerical simulation model.