Abstract: In order to study the influence of external longitudinal magnetic field on the droplet temperature, size and velocity of MIG welding, ER304 stainless steel wire was selected and argon was used as shielding gas, a two-dimensional axisymmetric droplet transfer numerical model considering external longitudinal magnetic field was established, the simulation results are in good agreement with the experimental results. The results show that when other welding parameters remain unchanged, the radial length of droplet at detaching time gradually increase and the axial length of droplet gradually decreases with the increase of the longitudinal magnetic field intensity within a certain range, the shape changes from long spherical to oblate spherical, and the transition frequency gradually decreases. But the effect of the external longitudinal magnetic field on the temperature and velocity of droplet is indirect and small.