The transient liquid phase diffusion bonding of GH5188 superalloy is carried out by using self-designed KCo8 cobalt-based interlayer. The effects of transient liquid phase diffusion welding process parameters on the microstructure of the joint are evaluated by means of Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and Electron Probe Micro-Analyzer (EPMA). The influence mechanism of welding process on the joint is explored. Moreover, the mechanical properties of the joint are evaluated by electronic universal testing machine, and the fracture mechanism is analyzed. The results show that the typical joint is mainly composed of three regions: GH5188 alloy (Base Metal), diffusion zone of precipitated phases such as M5B3 and M3B2, and isothermal solidification zone composed of cobalt-based solid solution. The diffusion behavior of the diffusion zone is related to the welding process. With the increase of the welding temperature or the prolongation of the holding time, the density of the precipitated phase in the diffusion zone gradually decreases. The optimum process parameters are welding temperature of 1 180 ℃ and holding time of 60 min. The average tensile strength of the joint is 1 033 MPa, which is 96.5% of the base metal, and is broken in the base metal, meeting the needs of the engineering background. This study provides a reference for the wide application of GH5188 TLP diffusion welding.