This paper studied the effect of shrinkage reducing admixture (SRA) on drying shrinkage and microstructure of alkali-activated coal gangue-slag (AACGS). Concrete was prepared by using calcined coal gangue as coarse aggregate. The effect of SRA on the compressive strength and durability of concrete under different calcined coal gangue coarse aggregate (CCGCA) content was investigated, and the action mechanism of SRA was also systematically analyzed. The research results showed that the addition of 3% SRA can reduce the drying shrinkage of AACGS mortar by 47.5%. The 28d compressive strength of concrete can be reduced by mixing with SRA, which has limited effect on the 90d compressive strength. SRA can significantly improve the frost resistance durability of concrete (water freezing and salt freezing conditions can increase the number of freeze–thaw cycles by about 50 and 25, respectively) and sulfate attack resistance (90d testing). With the increasing content of CCGCA, the effect of adding SRA on the improvement of anti-chloride penetration has become more obvious. SRA caused changes in the pore size distribution, reaction rate and interfacial bond strength of AACGS concrete. Moreover, the present study also provides the experimental and detailed theoretical basis for the action mechanism of SRA in alkali-activated materials concrete.