A seamless locking drain connector structure of a metallic sink is provided. A water outlet of a bottom of the metallic sink is integrally formed with an annular ring extending outward from the bottom of the metallic sink. The annular ring is fixedly connected with a connecting sleeve. The connecting sleeve is formed with outer threads. An open end of a stepped trough of the drain connector is formed with a retaining rim portion relative to the bottom end of the connecting sleeve. The retaining rim portion is connected with a locking sleeve. The locking sleeve is formed with inner threads corresponding to the outer threads of the connecting sleeve. The inner threads mesh with the outer threads, such that the retaining rim portion of the drain connector is tightly locked to the bottom end of the connecting sleeve to connect with the annular ring and the water outlet.