Objective Hydrogen blending into natural gas serves as a vital transitional pathway for green hydrogen consumption, low-carbon utilization of existing gas pipeline networks, and urban gas system transformation. Current research faces prominent limitations, including ambiguous boundary definitions for low, medium, and high blending ratios, insufficient systematic data of demonstration projects, inadequate gas interchangeability and end-device adaptability, and incomplete supporting standard systems. A systematic review of the current status, core constraints, and development trends of hydrogen blending into natural gas can clarify the technical limits and promotion strategies for hydrogen blending across diverse application scenarios.

Methods Literature review, engineering case comparison, and inductive analysis are adopted to summarize global research achievements on demonstration projects of hydrogen blending into natural gas, Power-to-Gas technologies, and pipeline compatibility. Relevant projects are selected to comparatively analyze their launch time, hydrogen blending ratios, application scenarios, and supply coverage scales.

Results The engineering feasibility of hydrogen blending is not determined by hydrogen volume fraction alone. Rather, it is jointly influenced by gas source composition, pipeline pressure rating, pipe material condition, end-use equipment, and regulatory requirements. Divergent technical routes adopted by various demonstration projects essentially reflect distinct variations in safety limits, monitoring conditions, and equipment transformation capacities across scenarios. Since low-pressure gas distribution systems directly supply residential and commercial consumers, progressive verification starting with low blending ratios is recommended. Enclosed areas—such as industrial parks, campuses, and islands—feature clear supply boundaries, making them suitable for accumulating long-term operational data and verifying the feasibility of integrated electricity-hydrogen-gas coordination. Conversely, industrial boilers, kilns, and gas turbines feature robust combustion adjustability, which can support medium-to-high hydrogen blending ratio trials and transitional verification toward pure hydrogen supply. Hydrogen blending alters key gas properties—including calorific value, Wobbe index, relative density, and flame propagation speed—and further exerts impacts on combustion stability, NOₓ emissions, energy metering, and material compatibility. Consequently, experience from existing projects cannot simply be replicated; scenario-specific assessments combining local gas sources, pipeline conditions, and end-use facilities are mandatory.

Conclusion Research on hydrogen blending into natural gas should shift from merely focusing on hydrogen blending ratios to system adaptation limits and risk control requirements for classified application scenarios, so as to formulate a hierarchical, phased scaling-up promotion roadmap. Future studies should establish a systematic evaluation mechanism that addresses full-process safety thresholds, equipment adaptability, operational monitoring, and low-carbon benefit accounting. This mechanism runs through the whole industrial chain from hydrogen injection to end utilization and spans engineering operation to standard formulation and supervision, thereby underpinning standardized and large-scale deployment of hydrogen blending into natural gas.