Abstract: In order to prevent molten iron to drop under gravity during all position MAG welding, an excitation device is developed on the base of eddy current effect, which can generate Lorenz force in weld pool. However, the power output of alternative electricity power is restricted at high frequency. Therefore, the excitation load circuit is researched. The inductive link is found in the circuit which results in inductive resistance large too much at high frequency. Then, the technology of series resonance is applied to decrease the effect of inductive resistance at high frequency. Experiment results show that this scheme can promote output of alternative electricity power. On the basis, the equivalent resistance and equivalent inductance are analyzed and studied, which is beneficial for excitation device power auto control.