The invention provides a numerically-controlled lathe tailstock automatic feeding control method capable of controlling the finishing of hole bottoms. A connecting device for realizing the automatic connection and disconnection of a saddle and a tailstock of a numerically-controlled lathe by using a cylinder, used in the invention, comprises a centering assembly, a rotating arm assembly, a driving assembly and a drill bit assembly, wherein the centering assembly comprises a centering shaft and a V-shaped block, the rotating arm assembly comprises a rotating arm, a rotating shaft, a shaft bushing and a gear wheel, the shaft bushing is fixed to the front side surface of the tailstock of the numerically-controlled lathe, the rotating shaft penetrates through the shaft bushing, the front end of the rotating shaft is fixedly connected with the rotating arm, the other end of the rotating shaft is fixedly connected with the gear wheel, a hook part capable of being clamped in an annular groove is arranged at the front end of the rotating arm, the driving assembly comprises a rack, a cylinder, an electromagnetic directional valve, a rack guide groove, a reset switch and a controller, the controller is mounted in a lathe power distribution cabinet and electrically connected with a numerical control system and the electromagnetic directional valve, and the reset switch is mounted on the front side of the saddle of the numerically-controlled lathe and is electrically connected with the controller.