Disclosed is an application method of a semicircular-pile stirring drill rig. When the semicircular-pile stirring drill rig works, a hydraulic motor drives a stirring shaft through a transmission case, a stirring drill rotates, a water jetting device jets high-pressure water, and the stirring drill cuts soil and stirs the soil and water into slurry during rotation; the hydraulic motor drives a left shaft and a first eccentric wheel to rotate through the transmission case, the first eccentric wheel pulls the left end of a semicircular frame body back and forth through a first eccentric wheel sleeve and a first transmission rod during rotation, the hydraulic motor drives a right shaft and a second eccentric wheel to rotate through the transmission case, the second eccentric wheel pulls the right end of the semicircular frame body back and forth through a second eccentric wheel sleeve and a second transmission rod during rotation, the semicircular frame body moves up and down by taking an inner tube as a guide shaft, a plurality of cutters cut the soil during movement of the semicircular frame body, a plurality of stirring cutters stir the soil and the water between a frame of the semicircular frame body and the stirring drill into slurry, and the slurry flows from a semicircular hole to be semicircular.