The invention provides a mounting device and a mounting method for a checking device of a connection pipe welding line of a steam generator. A steel wire suspension assembly is conveyed to a pipe plate in the steam generator by a long rod tool outside the steam generator and is fixedly arranged on the pipe plate; a steel wire rope is connected with the upper part of a middle rod by a pulley wheel; one end part of the checking device of the connection pipe welding line is connected with one end of the middle rod by a rotary joint I and the other end of the middle rod is connected with one end of an operation rod by a rotary joint II; the checking device of the connection pipe welding line and the middle rod are conveyed to the inner part of the steam generator by pulling the steel wire rope and pushing the middle rod and the operation rod; the operation rod is rotated around the axis of the operation rod so as to enable the checking device of the connection pipe welding line to be close to a welding line to be detected and then the scanning work is started. According to the mounting device and the mounting method for the checking device of the connection pipe welding line of the steam generator, the long rod tool composed of the operation rod and the middle rod and the steel wire rope are used for finishing the mounting of the checking device; a mounting part is simple and the operation is convenient; the mounting working amount and the exposure dose of workers are reduced.