The invention discloses a machining-positioning device and a machining method for a universal connecting shaft irregularly-shaped hole. The irregularly-shaped hole is a through hole provided with a round hole in the middle and irregular holes formed in two ends. The machining-positioning device comprises a pair of vices clamping the shaft end of a universal connecting shaft, a threaded jack supporting the ball end of the universal connecting shaft and a positioning plate arranged under the universal connecting haft irregular hole and further comprises positioning pins matched with a positioning hole and the round hole, wherein the positioning hole coaxial with the round hole of the irregular hole is formed in the positioning plate. The machining method utilizes the positioning device to achieve machining of the universal connecting shaft irregularly-shaped hole. By means of the machining-positioning device and the machining method, the irregular holes formed in two ends of the irregularly-shaped hole are consistent in machining-positioning standard, the coaxiality of irregular holes formed in the upper end and lower end of the universal connecting shaft irregularly-shaped hole is ensured, and machining accuracy of the holes is further ensured. Two sides of the universal connecting shaft bear consistent twisting force during transmission, the universal connecting shaft is stable in transmission, and the service life of the universal connecting shaft is prolonged.