The utility model discloses a high temperature gas cooled piles steam outlet connecting pipe pipe clamp pretension force measuring device and corresponding methods of measurement, the device include pipe clamp and two pipe clamp frocks, and the pipe clamp is including two blocks of L template materials assembling into rectangular frame be provided with resistance strain gauge on rectangular frame's the surface, the pipe clamp frock is used for tightening the pipe clamp frock is removed to the connecting pipe after pipe clamp welding is accomplished, read the value of meeting an emergency of pipe clamp through the electronics foil gage on the pipe clamp, and then know the remaining pretightning force on the pipe clamp, through changing the welding parameter, duplicate test many times can obtain multiunit welding process parameter and the remaining pretightning force value information that corresponds to can select the welding parameter that can produce the remaining pretightning force that meets the requirements as required.