The invention discloses a bridge construction punching device and a punching method thereof. The punching device comprises a bracket and a second motor, wherein the bracket is fixed at the top end ofa pile hole through a fixing steel brazing, a sliding sleeve is fixedly arranged in the middle part of the bracket in a welding mode, an ejector rob is movably arranged in the sliding sleeve, the ejector rob is formed by combining a plurality of ejector rob units, and a toothed plate is fixedly arranged on one side of the ejector rob unit in a welding mode. The bracket is provided with a first motor through a motor support, a driving gear is fixedly connected with the output end of the first motor, and the driving gear meshes with the toothed plate. A rotating shaft is connected with the output end of the second motor through a speed reducer, and a cutter head is fixed on the rotating shaft. The cutter head is driven to rotate by the second motor, the pile hole can be excavated, the lengthof the ejector rob can be increased by adding the ejector rob units step by step, the ejector rob is transported downwards by the first motor, and the cutter head is pushed to dig downwards. The drilling depth can be effectively increased, the operation is simple, and the practicability is high.