Abstract: First of all, the symmetric component method is applied to the asymmetric faults research in neutral ungrounded grid to calculate the after-fault current and voltage, and the physical meaning of neutral point deviation is clearly explained by using zero sequence network. Then, the distribution of negative sequence and zero sequence components in unsymmetrical faults of neutral earthed and ungrounded networks is systematically introduced, and the ground short circuit and disconnection faults are carefully analyzed in comparison.