The invention discloses a pier construction method of a full-prefabricated bridge girder erection machine and a via hole method thereof. The construction method comprises the steps that 1, the bridgegirder erection machine transversely moves to one side, then feeds a (Pn+3)th pier from the rear end of the bridge girder erection machine and conveys the pier to a (Pn+3)th pier foundation, and the (Pn+3)th pier on one side is erected at first; 2, the bridge girder erection machine transversely moves to the other side, then feeds the other (Pn+3)th pier from the rear end of the bridge girder erection machine, and conveys the (Pn+3)th pier to the (Pn+3)th pier foundation, and the (Pn+3)th pier on the other side is erected; 3, after the (Pn+3)th pier is grouted, and the requirement for the strength is met, the bridge girder erection machine transversely moves to the midcourt line, then feeds a (Pn+3)th bent cap from the rear end of the bridge girder erection machine, and conveys the (Pn+3)th bent cap to the portion between the two (Pn+3)th piers, and the (Pn+3)th bent cap is rotated horizontally by 180 degrees, and erected on the two (Pn+3)th piers in a crossing mode; the method is quite suitable for peri-urban areas and places with complex construction conditions and large construction environment traffic pressure for rapid erection of overground part overpasses such as urban roads, urban light rails and subway lines.