Compressive strength, flexural strength test, water absorption test, drying shrinkage test, SEM and FTIR were used, in order to study the effects of different alkali equivalents, different fly ash and slag content on the mechanical properties, drying shrinkage and microstructure characteristics of alkali-activated fly ash-slag mortar. The results show that: at the age of 3 d, 7 d and 28 d, with the increase of alkali equivalent and slag content, the compressive strength and flexural strength of fly ash slag mortar gradually increase, while the water absorption and drying shrinkage rate decrease gradually. When the age is 28 days, the alkali equivalent is 6%, and the slag content is 100%, the compressive strength of alkali activated fly ash slag mortar reaches the peak value of 110.84 MPa, the flexural strength reaches the peak value of 10.77 MPa, and the minimum water absorption rate is 1.2%, compared with the 4% fly ash slag mortar, the drying shrinkage of the mortar with alkali equivalent of 6% is reduced by more than 10%. According to the microscopic analysis, the hydration products of fly ash-slag mortar under the action of alkali are mainly aluminosilicate gel and hydrated calcium silicate gel. The greater the amount of fly ash, the lower the gel crystallinity. The greater the alkali equivalent, the greater the number of hydration products in the system and the denser the structure.