A modified Gaussian current density is put forward, which is used to simulate the dynamic process of AZ31B magnesium alloy double-electrode gas metal arc welding (DE-GMAW) droplet transfer. The process of droplet transfer in the AZ31B magnesium alloy DE-GMAW was simulated using FLUENT software. The influence of different bypass welding currents was investigated with a constant total current. The simulated results revealed that when the bypass current was 0 A, the process was the globular transfer type, the droplet transfer with a bypass current of 80 A was a projected transfer type and the droplet transfer at a bypass current of 170 A was a spray transfer type. The critical current is decreased so that spray transfer would occur at a lower current level in the DE-GMAW process. As the bypass current was increased, the shape of droplet changed from oval to round and the transition frequency of the droplet increased in a stepwise fashion. To confirm the accuracy of the simulated results, welding experiments were performed and the image processing method was used to obtain the droplet size. The simulated and experimental results were found to be in good agreement.