The utility model discloses a large shaft diameter measuring and detecting device, which is characterized in that a measuring scale penetrates through the middle of a shell, support rods are respectively arranged at two ends of the shell, the length directions of a first support rod and a second support rod are the same as the length direction of the measuring scale, and rollers are hinged to thelower ends of the support rods. The device further comprises a first rack and a second rack; the first rack and the second rack are slidably connected into the shell, one end of the first rack extendsout of the end of the shell to be connected with the first supporting rod, one end of the second rack extends out of the other end of the shell to be connected with the second supporting rod, and thefirst rack and the second rack are in gear engagement transmission. The large-shaft-diameter measuring and detecting device is simple in overall structure and low in manufacturing cost; a measuring head of the measuring scale penetrates through the center of the measured cylinder; the actual size of the large shaft diameter is obtained through the reading of the measuring instrument; and the pinroller is in linear contact with the cylindrical surface of the measured shaft diameter, so that the wear resistance is improved, the stability of the workpiece is maintained, and the precision of themeasuring device is further ensured.