The invention relates to a method for processing the singularity of a transformer three-phase node admittance matrix. The method comprises the steps that first the relation of three-phase voltages and zero sequence voltages and the relation of three-phase currents and zero sequence currents are established according to the wiring mode of a transformer winding, the relation of the three-phase voltages and the zero sequence voltages is used as an additional condition to constitute a new transformer three-phase node voltage equation with an original transformer three-phase node voltage equation; a least square method is used for the new transformer three-phase node voltage equation to obtain a new transformer three-phase node admittance matrix which includes the information of an original transformer three-phase node admittance matrix and also includes the relation of the three-phase voltages and the zero sequence voltages and the relation between the three-phase currents and the zero sequence currents. The method for processing the singularity of the transformer three-phase node admittance matrix solves the calculating problem caused by the singularity of the transformer three-phase node admittance matrix in calculation and analysis of a multiple-voltage-class power distribution network.