In order to realize the large-scale resource utilization of red mud and low-impact construction of highway engineering environment, red mud-based cementitious materials were prepared by red mud, blast furnace slag and ordinary Portland cement. The effects of raw material ratio on the setting time, rheological properties, compressive strength and volume stability of red mud-based cementitious materials were studied. The hydration process, reaction product type and micro-morphology characteristics were revealed, and the mechanical properties and environmental protection properties of red mud-based cementitious materials stabilized macadam base were discussed. The results showed that with the increase of red mud content, the setting time of cementitious materials was shortened first and then prolonged, the 28 d compressive strength was gradually reduced, and the dry shrinkage rate gradually decreased. When the red mud content was 45%, the initial setting time was 226 min, the 28 d compressive strength was 32.6 MPa, and the 28 d shrinkage rate was 0.128%, which can meet the requirements of road base construction. Rheological performance tests showed that the increase of red mud content can improve the structural stability of the slurry, which was manifested by the increase of yield stress and the decrease of plastic viscosity. The microscopic analysis showed that the alkaline substances (NaOH, Na₂CO₃) in red mud can promote the reaction between cement hydration and the pozzolanic reaction of blast furnace slag, and generate zeolite-like, C-S-H gel, silica calcite and other reaction products. The hydration products cross each other to form a crystal gel wrapped structure, which increases the compactness of the system. The test of stabilized gravel base showed that when the content of red mud-based cementitious material was 5%-7%, the 7 d unconfined compressive strength was 5.8-7.2 MPa, which can meet the requirements of extremely heavy and extra heavy traffic intensity on highways. The leaching test showed that the leaching amount of Na⁺ and total Cr was lower than the class III limit of 'Groundwater Quality Standard', and the environmental risk was controllable.