Abstract: The large stock，large increment and low utilization rate of coal⁃based solid waste generated in coal mining， power generation， coal chemical industry and other industries have become a bottleneck restricting the green， low⁃carbon and high⁃quality development of the Ningdong base. Underground green backfilling is an effective way for harmless，resourceful and large⁃scale disposal and utilization of multi⁃source coal⁃based solid waste. Taking the Ningdong base as the pilot area，this paper analyzes the pollution risk，physicochemical properties and multiple attrib⁃ utes of multi⁃source coal⁃based solid waste，and systematically expounds the basic theory and technical system of coal⁃ based solid waste for underground backfilling. The research shows that:1 The pollution and physicochemical proper⁃ ties of coal gangue，fly ash，desulfurization gypsum，etc. conform to the landfill standard (GB 18599—2020)，and the content of some heavy metals in gasification slag，furnace bottom slag exceeds the screening value，and the po⁃ tential pollution risk can be reduced by taking some technical measures. Multi⁃source coal⁃based solid wastes can be used for underground green backfilling. 2 The basic theory of coal⁃based solid waste for underground backfilling in⁃ cludes the feasibility evaluation of green backfilling，the characteristics of backfilling materials from coal⁃based solid waste，the multi⁃field coupling mechanism between backfilling materials and the environment，and the multi⁃ layer three⁃dimensional backfilling mode.3 The green backfilling technology system of multi⁃source coal⁃based solid waste mainly includes precise mining technology of coal gangue source reduction，integrating underground mining⁃sepa⁃ rating⁃backfilling coordination technology，heavy metal adsorption and complex passivation technology for coal⁃based solid wastes，preparation technology of backfilling materials from multi⁃source coal⁃based solid waste，long⁃distance pipeline transportation technology of backfilling materials， intelligent monitoring technology of whole backfilling process，etc. 4 Finally，according to the geological conditions of the Renjiazhuang Mine in the Ningdong base，ad⁃ vanced borehole backfilling and low⁃level backfilling are proposed and implemented. The new multi⁃industry chain col⁃ laborative utilization mode of coal⁃based solid waste is prospected， which integrates the preparation of active powder，the research and development of high⁃value building materials，ecological restoration and treatment，and under⁃ ground green backfilling.