An automatic tin-adding machine for adding a plurality of tin rods to a molten tin tank comprises a base, two transmission shafts, at least one first flexible transmission member, a plurality of tin rod carrying members, a tin stock detector, a drive and a circuit control system. The base has a tin rod adding opening corresponding to the molten tin tank. The two transmission shafts are pivoted on the base side by side. The at least one first flexible transmission member is sleeved on the two transmission shafts. The tin rod carrying members are fixed to the first flexible transmission member and configured to carry the tin rods. The tin stock detector is configured to detect the stock of tin liquid in the molten tin tank. The drive is connected to one of the transmission shafts. The circuit control system comprises a circuit control unit.