Based on the surface shot peening treatment of Hastelloy X, this study investigates the impact of shot peening on the interfacial element diffusion and properties of wide-gap brazing joints. The microstructure and mechanical properties of wide-gap brazing joints obtained from Hastelloy X surfaces without shot peening and those treated with shot peening using ball sizes of 0.180mm, 0.300mm, and 0.500mm were compared. SEM and EDS were utilized to analyze the diffusion layer structure and element distribution characteristics. The results indicate that the grain refinement effect from shot peening strengthening treatment promotes the diffusion of the melting-reducing element Si in Hastelloy X. When the shot size is 0.300mm, the diffusion coefficient of Si in the brazing joint structure is the highest, at 1.83×10-8mm2s-1; at this time, the diffusion layer is the thickest, at 224.97μm; the interface shear strength of the wide-gap brazing joint is the greatest, at 543.38MPa, which is a 19.39% increase compared to the non-shot-peened sample. Additionally, theoretical calculations were conducted to determine the impact of different grain sizes under three shot peening processes on the diffusion coefficient of Si element, combining theoretical calculations with experimental data to elucidate the diffusion mechanism of Si in the microstructure of wide-gap brazing joints.