The invention relates to a synchronous transmission device and a 1*7 and 1*19 hybrid steel strand production line, aiming to provide a synchronous transmission device and a production line in which a rope skipping type strander and a tubular type strander are connected to realize production of a 1*7 and 1*19 hybrid steel strand and to reduce the production cost. In the synchronous transmission device, a transmission shaft of the tubular type strander is respectively connected with one end of a first elastic coupling and one end of a second elastic coupling; the other end of the first elastic coupling is connected with the output shaft of a variable frequency alternating current machine for driving the tubular type strander; the other end of the second elastic coupling is connected with the input shaft of a split type synchronizing gear transmission mechanism; a third elastic coupling is respectively connected with the transmission shaft of the rope skipping type strander and the output shaft of a variable frequency alternating current machine driving the rope skipping stranding machine; the other end of the rope skipping type strander is connected with a constant torque friction disc; and two ends of a universal joint shaft are respectively connected with the constant torque friction disc and the output shaft of the split type synchronizing gear transmission mechanism.