Abstract: The transition from traditional fossil fuels to the widespread use of hydrogen energy marks a critical phase in energy evolution. Hydrogen/methane mixtures, serving as crucial carriers of hydrogen energy, play a key role in this process. However, the high risk of spontaneous ignition during high-pressure hydrogen leakage poses a significant safety challenge. Incorporating small amounts of methane into hydrogen can reduce this tendency, thereby enhancing the safety of high-pressure storage and transportation. Spontaneous ignition is triggered by abrupt localized temperature rises caused by shock waves during leakage; these shock waves are fundamental in determining the ignition characteristics of hydrogen/methane mixtures. Methane blending significantly changes shockwave behavior, affecting their propagation, and the resulting temperature and pressure changes influence spontaneous ignition; however, the underlying mechanisms of these effects remain unclear. This paper focuses on the evolution and characteristics of shock waves in high-pressure hydrogen/methane mixture leakage using an improved experimental system for spontaneous ignition research. Experimental results indicate that upon bursting disc rupture, a leading shock wave forms in the discharge tube, and as the shock wave propagates, the distance between the leading shock wave and the main jet of the hydrogen/methane mixture gradually increases. Simultaneously, the shape discontinuity between the circular rupture and the rectangular discharge tube creates reflected shock waves at the corners, developing into complex multidimensional shock waves reflected within the discharge tube. Leakage pressure and methane blending ratio significantly impact shock wave characteristics. Higher leakage pressures increase shock wave pressure and propagation velocity, whereas greater methane blending ratios reduce them. Using shock tube flow theory and the physical property database of National Institute of Standards and Technology, a calculation model was developed to predict shock wave parameters during hydrogen/methane leaks. A comparative analysis with literature and experimental data confirmed the applicability of the optimized calculation model for shock wave characteristic parameters in high-pressure hydrogen/methane mixture discharge scenarios. Spontaneous ignition reactions within the rectangular tube influence internal pressure dynamics. When burst pressure is below the critical threshold for ignition, during the leakage process of high-pressure H₂/CH₄ mixture, the pressure at sensor P2 exceeds that at P3 during leakage. Conversely, when the pressure is far above this threshold, spontaneous ignition occurs within the rectangular tube and develops into intense combustion near P3, subsequently elevating the pressure at P3, manifesting as P3 > P2. At pressures slightly above the critical threshold, the pressure relationship between P2 and P3 depends on the methane ratio. These findings provide a theoretical foundation for understanding spontaneous ignition phenomena during hydrogen/methane leakage and serve as a reference for future experimental designs.