Middle support leg of segment assembly bridge girder launcher is made up of hanging system, roller institution, core plate, bracket cross girder, upright, driving gearbox ofsegment assembly bridge girder launcher lateral moving system, driven gearbox, fixed locking device, lateral moving rail and pins.

Middle support leg is important support of the machine. Middle support leg can moves forward automatically with hanging system, drive main girder to cross piers stably and move forward with roller institution; make the complete machine move laterally along the rail with lateral moving gearbox and lateral sliding rail; adjust angle with core plate for the convenience of curved bridge and skewed bridge construction; bracket cross girder makes left leg and right leg connect together.

Sliding rail of middle support leg is anchored with bridge deck or abutment when the bridge girder launcher cross piers and install girders.