The invention relates to the field of repair of nodular iron castings and discloses a welding and mending method for a nodular cast iron workpiece. The method comprises the following steps: S1, afterheating the vicinity of the integral workpiece or the defected part to a certain temperature, heating the defected part of the workpiece to a melting temperature; and S2, heating a nodular cast iron welding rod identical to or similar to the workpiece in material to a melted state, dropwise adding the molten nodular cast iron welding rod into the defected part, and keeping the temperatures of themolten nodular cast iron welding rod and the defected part which are combined being identical or similar. The invention aims to provide a nodular cast iron welding and mending method which is small inworkload and simple to operate, the repaired part is free of color difference and the strength is not deteriorated. No defect is found in the workpiece, on the surface of the workpiece and at the combined part of the workpiece through ultrasonic flaw detection and magnetic powder inspection on the welded and mended part and the periphery of the welded and mended part.