The invention discloses a timing chain assembling method and a timing chain assembling device, which comprises a first feeding tray, a second feeding tray and a third feeding tray. A chain link step type assembly mode is adopted; the first feeding tray is in an operating state all the time and pushes base plates, pin shafts and inner plates to assembly stations for pressing assembly; the second feeding tray and the third feeding tray enter an operating state at the same time; the second feeding tray stays in an operating state when a mark plate is not assembled and pushes a cover plate to an assembly station for pressing assembly, and when the mark plate is assembled, the second feeding tray enters an idle state and does not push the cover plate; and when the mark plate is not assembled, the third feeding tray is in an idle state and does not push the mark plate, but when the mark plate is assembled, third feeding tray is in an operating state and pushes the mark plate to an assembly station for pressing assembly. According to the technical scheme, the timing mark plates are arranged on the timing chain at positions at different link intervals while the chain is assembled automatically, the processing efficiency is increased and the quality of the chain is ensured.