The purpose of automatic bit feed is to keep the designed constant pressure value of bit weight at the bottom hole and achieve optimized drilling. The current automatic bit feed of deep and ultra-deep drilling rig is realized by winch, top pulley, swimming pulley, wire rope and hook; as the dynamic load of winch and hoisting system, the vibration of wire rope and the obvious uneven speed of bit feed by hook make bit weight at the bottom hole unstable and accurate bit feed is difficult. The paper describes the working principle of bit feed by hoisting system and the methods of automatic bit feed by hydraulic disc brake and auxiliary motor. It is put forward that the ideal solution for accurate automatic bit feed is to use the hydraulic cylinder system. By hydraulic cylinder lift rig without winch system, hydraulic cylinder system can automatically fulfill bit feed and round trip; and winch and hydraulic cylinder can be separately used for round trip and automatic bit feed to eliminate the interference of winch and hoisting system to automatic bit feed.