The invention discloses a connecting device suitable for a forging die for a large upsetting forging crankshaft and a using method thereof. The connecting device comprises a connector, wherein the connector is I-shaped, and the upper end of the connector is fixed on a sliding block of a press; a pair of shaft tables are arranged at the lower end of the connector, and shaft holes are formed in theshaft tables; connecting shafts penetrate through the shaft holes in a penetrating mode, and elastic check rings are arranged at the two ends of the connecting shafts; bosses with the position corresponding to the that of the connector is further arranged at the lower end of the connector; connecting pieces are also in an I-shaped shape and each comprise an upper cross arm and a lower cross arm, wherein through holes are formed in the upper cross arms, and the through holes are connected with the connecting shafts in an axial mode, and the lower parts of the upper cross arms are planes and arematched with the upper surfaces of the bosses; the upper parts of the lower cross arms are matched with the upper side surfaces of grooves arranged on the die; and pin holes are formed in the upper surface of the die and the lower surface of the connector correspondingly, and positioning keys are inserted into the pin holes. The connecting device and the using method thereof have the advantages that a traditional structure utilizing bolt conduction force can be changed into a large-scale rectangular cross section conduction structure with the connecting pieces, so that the connecting strengthis high, structure is simple, operation is convenient, and working stability and the safety of the die are high.