The invention discloses a restoring method of easily-damaged parts such as a steel cylinder, a threaded rod and a melt filter in plastic machines. Before and after damaged easily-damaged parts are restored, surface blots are processed, and grinding and polishing are performed. The method is characterized in that the hole diameter of an inner hole of the damaged steel cylinder is enlarged through a boring mill, and a machined steel cylinder inner hole is accurately ground through a grinding machine; surfacing welding is performed on continuous threads of the damaged threaded rod through a direct-current welding machine and stainless steel electrodes, the maximum outer diameter size of the damaged threaded rod is increased, the maximum outer diameter size, matched with the hole diameter of the inner hole of the restored steel cylinder, of the threaded rod is determined, and circular grinding is performed on the maximum outer circle of the threaded rod through the grinding machine; the damaged melt filter is heated, remaining materials molten on the surface are removed, the surface of the melt filter is polished; and the restored easily-damaged parts need to be subjected to surface nitridation, the depth of nitridation layers is 0.1-0.18 mm after the surfaces of the easily-damaged parts are subjected to nitridation, the surface hardness of the restored workpieces can reach HV850-1200, the restoration procedure is simple, and cost is low.