The invention discloses a method for detecting the concrete beam anchor lower prestress and a device for realizing the method. The device for detecting the concrete beam anchor lower prestress is arranged on an anchor rope of a concrete beam, which is tensioned and is not grouted; and a working anchor is locked at the root part of the anchor rope extending out of the concrete beam. The device comprises a counter-force cylinder, a through jack and a working anchor which are sequentially arranged on the anchor rope in a serial mode; the counter-force cylinder is sleeved outside the working anchor; the bottom of the counter-force cylinder is open; an opening surface is attached to and bears a concrete beam section of the working anchor; the top of the working anchor is provided with a through hole for the anchor rope to pass through; the jack is arranged on the top surface of the counter-force cylinder for tensioning the anchor rope; the working anchor is installed on the jack for locking the anchor rope; and the device also comprises a displacement and load tester which is connected to the anchor rope in series and is positioned between the counter-force cylinder and the working anchor. The method for detecting the concrete beam anchor lower prestress and the device for realizing the method can standardize the quality control behavior of a prestress bridge and improve the integral quality level of the prestress bridge.