The soil and groundwater in Northwest China contain a large number of aggressive sulfate ions, magnesium ions and chloride ions, which leads to the durability degradation of in-service recycled aggregate concrete (RAC), and seriously restricts the use of RAC in new structures in Northwest China. In order to study the durability degradation law of RAC with multiple cementitious materials system subjected to compound salt erosion, the durability failures of different parts of RAC structural components were simulated by three modes: full immersion, partial immersion, alternating dry and wet immersion, and the durability tests of compound salt erosion of RAC were carried out. Taking the relative dynamic elastic modulus, weight loss rate and relative compressive strength as the indicators, the durability degradation law of RAC subjected to compound salt erosion under different erosion modes was studied, and the influences of the matching mode and replacement rate of supplementary cementitious materials in multiple cementitious materials system on the durability degradation law of RAC were analyzed. Under the full immersion mode, the relative dynamic elastic modulus of fly ash-slag double-mixed RAC decreases slowly. Under the partial immersion mode, the introduction of supplementary cementitious materials reduces the resistance of RAC to compound salt erosion. Under the alternating wet and dry immersion mode, the physical and mechanical properties of RAC increase first and then decrease, and the multiple cementitious materials system RAC shows better resistance to salt erosion than that of pure cement RAC.