Abstract: The printed circuit heat exchanger (PCHE) is welded by diffusion welding, but the existence of the heat exchange flow channel causes the interruption of the transmission of welding pressure along the heat exchange plate, resulting in the non-welding in the middle of the flow channel. In order to improve the welding quality, the optimization of the runner structure is carried out. The research results show that increasing the chamfer of the rectangular runner is beneficial to improve the welding quality. Dislocation of the hot and cold runners (to place the lower runner aid plate in the middle of the upper runner) can also change the axial stress distribution between the plates to improve the welding quality.