Abstract: The printed circuit heat exchanger (PCHE) has a multilayer, thin-walled, micro-channel structure. Solving the problem of achieving its high-quality connection is urgently needed. 316L stainless steel is commonly used to manufacture PCHE due to its excellent mechanical properties, weldability, and corrosion resistance. In this study, vacuum diffusion bonding was used to connect 316L stainless steel. The optimal process parameters of the diffusion bonding process were explored, and the relationship between the process parameters, interface structure, and mechanical properties was established. With increasing bonding temperature and holding time, the bonding rate, grain size, and deformation rate of the joints continue to increase, while the hardness continues to decrease. The tensile shear strength initially increases and then decreases. A temperature of 1000 ℃, time of 60 min, and pressure of 10 MPa are the optimal parameters, giving a maximum joint strength of 626 MPa. The fracture morphology of the bonded joint was a dimple pattern with features of ductile fracture.