Abstract: To achieve large−scale resource utilization of coal−based solid wastes and mitigate the environmental pollution and land occupation caused by long−term stockpiling, this study develops a coal gangue−based reclamation substrate without adding external soil. Coal gangue is used as the primary material, while fly ash, coal gasification slag, rice husk biochar, and xanthan gum are incorporated as composite amendments. An L9（3⁴） orthogonal experiment with four factors and three levels is conducted to investigate the effects of amendment dosages on the physical properties of the coal gangue−based substrate and determine the optimal formulation.The results showed that biochar exhibited the greatest influence on total porosity and field water−holding capacity, with maximum values of 47.89% and 24.64%, respectively. Xanthan gum had the most significant effect on water−stable macroaggregate content, which reached a maximum value of 76.51%. Based on the comprehensive scoring method, the optimal amendment ratio was determined as 4% fly ash, 4% coal gasification slag, 8% biochar, and 0.6% xanthan gum. Compared with untreated coal gangue, the optimized formulation significantly increased the total porosity, field water−holding capacity, and water−stable macroaggregate content of the substrate, with improvements of 25.4%, 157%, and 42.5%, respectively.Microstructural mechanism analysis indicated that during the modification process, the coal gangue−based substrate maintained the basic stability of the Si–Al framework mineral structure, while particle rearrangement and cementation occurred, resulting in enhanced interparticle bonding strength and overall structural stability. These findings provide scientific support for the resource utilization and large−scale engineering application of coal gangue and offer a feasible technical pathway for its practical application in ecological restoration and soil improvement.