The invention relates to an automatic feeding device for a tapping machine. The automatic feeding device comprises a rack assembly, a conveying belt assembly, a guide rail assembly, mechanical arm assemblies and a control cabinet assembly. The conveying belt assembly is mounted on the rack assembly. The guide rail assembly is mounted on the rack assembly and communicates with the conveying belt assembly. The mechanical arm assemblies are mounted at the two sides of the guide rail assembly. The control cabinet assembly is used for controlling the machine to conduct tapping. According to the automatic feeding device for the tapping machine, materials are conveyed to the guide rail assembly through the conveying belt assembly and clamped and conveyed to guide rails under the tapping machine in groups through the mechanical arm assemblies; at the moment, tapping is conducted on the group of materials through the tapping machine; subsequently, the mechanical arm assemblies continue to clampthe next group of materials and push the materials obtained after tapping out of the guide rails; in this way, automatic feeding and tapping of the tapping machine are achieved; the automation degreeis high; safety and reliability are achieved; and manpower is saved.