Abstract: In the transitional phase from traditional fossil fuels as the primary energy source to large-scale application of hydrogen energy, hydrogen/methane mixture, serving as a crucial carrier of hydrogen energy, constitutes an essential part of the hydrogen energy application system. The high propensity for spontaneous ignition during high-pressure hydrogen leakage poses a threat to the large-scale adoption of hydrogen energy. Incorporating a small amount of methane into hydrogen can reduce its spontaneous ignition tendency to a certain extent, thereby enhancing the safety of high-pressure storage and transportation of hydrogen energy. The abrupt temperature rise in localized regions caused by shock waves during leakage is the direct cause of spontaneous ignition in hydrogen/methane mixture, indicating that the shock waves during leakage a key factor determining the characteristics of spontaneous ignition. Therefore, this paper focuses on the evolution process and characteristic parameters of shock waves during the leakage of high-pressure hydrogen/methane mixture, conducting experimental research based on an improved experimental system for spontaneous ignition of high-pressure flammable gas leakage. Experimental results indicate that upon bursting disc rupture, a detached leading shock wave is initially formed within the discharge tube, and as the shock wave propagates, the distance between the leading shock wave and the main jet of hydrogen/methane mixture gradually increases. Simultaneously, due to the shape discontinuity between the circular rupture and the rectangular discharge tube, reflected shock waves first emerge at the corners of the rectangular tube, ultimately forming complex multidimensional reflected shock waves within the discharge tube. Leakage pressure and methane blending ratio significantly impact shock wave characteristics. Specifically, as the leakage pressure increases, shock wave pressure and propagation velocity notably increase, whereas they decrease markedly with an increase in methane blending ratio. Based on shock tube flow theory and the NIST physical property database, a calculation model for shock wave characteristic parameters during high-pressure hydrogen/methane mixture leakage is established. Comparative analysis with literature data and experimental data in this paper confirms the applicability of the optimized calculation model for shock wave characteristic parameters in high-pressure hydrogen/methane mixture discharge scenarios. The research findings provide a theoretical basis for understanding spontaneous ignition phenomena during high-pressure hydrogen/methane mixture leaks and offer reference for related experimental designs.