Abstract: To address the challenges of roadside support of non-pillar coal mining and the environmental pollution from coal-based solid waste accumulation during the green development of coal resources in the Yellow River Basin, as well as the limitation of traditional concrete’s heavy consumption of non-renewable resources such as natural sand and gravel, this paper integrates practical application requirements, aims to replace natural sand and gravel with coal gangue to produce coal gangue aggregate concrete, thereby reducing the consumption of natural sand and gravel and enabling the resource utilization by returning underground of coal gangue solid waste. Washed coal gangue with particle sizes of 3-6 mm and 6-13 mm are selected as the research aggregate. The physical properties of the coal gangue, including bulk density, water absorption, crushing index, and particle size distribution, are first tested. On this basis, coal gangue aggregate concrete of different strength grades is prepared, and its mechanical properties, interfacial transition zone （ITZ） characteristics, and micromorphology are systematically investigated. The cementation characteristics of the coal gangue aggregate concrete and their influence mechanism on strength are further revealed, providing a scientific basis for optimizing the particle morphology and particle size distribution of the coal gangue aggregates. The results show that the interfacial bonding properties between the coal gangue aggregate and the cement paste are key factors influencing the concrete strength. By optimizing the particle size distribution of the coal gangue aggregate, the compactness of the interfacial transition zone （ITZ） can be effectively improved, thereby enhancing the overall mechanical properties of the concrete. Based on the above research, the mix proportions of C30 and C40 coal gangue aggregate concrete are determined, and the technical pathways for the resource utilization by returning underground of coal gangue aggregate concrete is proposed, thus achieving the underground backfill application of coal gangue. This provides a new material for roadside support non-pillar coal mining and offers an engineering practice reference for promoting the green development of coal resources in the Yellow River Basin.