Abstract: The heat transfer core of the printed circuit heat exchanger is made of stacked hot and cold heat exchange plates by diffusion welding at high temperature and high pressure.However, the existence of heat exchange runner hinders the uniform transmission of welding pressure along the heat exchange plate, resulting in uneven distribution of axial stress between the plates and poor welding quality at the runner, deformation of the laminate and other defects.Considering the flow geometry size (runner width, rib width, plate thickness)and welding pressure, the distribution law of the axial stress between the welded interface of heat exchange plates was studied by using the finite element method. The results show that the absolute value of the axial stress between the plates shows the distribution of first decreasing then increasing from one side to the other within one flow channel width. The central area of the channel is the weak welding area. The axial compressive stress between the plates decreases with the increase of the channel width, which is not conducive to welding. With the increase of plate rib width and welding pressure, the axial compressive stress between plates increases, but the stress concentration at both sides of the channel intensifies, which is easy to produce welding deformation. The axial stress distribution of the runner interface is more uniform by appropriately increasing the thickness of the runner plate.