The invention discloses a three-machine three-strand slab continuous casting machine production line which is specially matched with the rapid smelting period of a large converter. Three water outlets are formed in the bottom of an intermediate tank of the production line. A one-strand slab continuous casting machine is correspondingly arranged on the lower portion of each water outlet. The two sides, in the inner and outer arc direction, of each vibration device are each provided with a vibration oil cylinder and leaf springs, wherein the two vibration oil cylinders are set to be the same in motion stroke, and the leaf springs are set to be the same in mounting angle. All loads of the vibration devices are transmitted to a secondary cooling chamber concrete wall through vibration supporting structures. Sector segment transmission devices of the casting machines on the left side and the right side are arranged outside the secondary cooling chamber concrete wall, and motors and speed reducers are directly connected with drive rollers of horizontal sector segments through couplers. A transmission device of the middle slab continuous casting machine is a suspended transmission device. Productivity can be obviously increased, existing two-strand continuous casting machines can be conveniently modified into three-machine three-strand continuous casting machines, the process layout is compact, and the economic performance is excellent.