The utility model provides a gas -gas heat exchanger, including the top tube sheet, the bottom tube sheet, and a frame, spacing pipe strap and bellows, the frame is installed to top tube sheet lower extreme, the bottom tube sheet is installed to the frame lower extreme, the top tube sheet is connected with the bottom tube sheet through the frame, bottom tube sheet upper end is equipped with the bellows, the bellows sets up at the frame inboardly, install spacing pipe strap on the bellows, the assembly of spacing pipe strap is inner at the frame, the assembly of spacing pipe strap is at bottomtube sheet upside, the assembly of spacing pipe strap is at top tube sheet downside, top tube sheet lower extreme is equipped with the bellows, heat transfer area can be extended in this design, the utility model discloses have the function of freely stretching out and drawing back, job stabilization nature is good, and long service life extends heat transfer area, has reduced the heat exchanger cost.