In response to the problem of shrinkage and cracking of alkali-activated slag cementitious material， a new type of micrometer sized fiber—calcium carbonate whisker was used to reduce drying shrinkage and enhance mechanical properties of alkali-activated slag cementitious material. The effects of different contents of calcium carbonate whiskers on the rheological properties， compressive strength and drying shrinkage of alkali-activated slag cementitious material were studied， and the micro reinforcement mechanism was explored. The results show that the addition of micrometer sized calcium carbonate whisker has little effect on the fluidity of alkali-activated slag cementitious material. When the calcium carbonate whiskers’ content is 3%， the plastic viscosity of the freshly mixed slurry is 12.33 Pa·s， which is only 14.48% higher than the control group without calcium carbonate whiskers. The 28 d compressive strength of the hardened slurry reaches 105.8 MPa. The drying shrinkage rate of alkali-activated slag cementitious material decreases with the increase of calcium carbonate whiskers’ content. When the calcium carbonate whiskers’ content is 5%， its 28 d drying shrinkage rate is only 0.87%， which is 32.56% lower than that of alkali-activated slag cementitious material without calcium carbonate whiskers. Calcium carbonate whiskers are tightly combined with the matrix， dispersing the stress on the matrix when it is subjected to stress and improving the mechanical properties of alkali-activated slag cementitious material. The bridging effect of calcium carbonate whisker can effectively delay the formation and propagation of microcracks in alkali-activated slag cementitious material， and the development of macroscopic crack can be restrained to a certain extent.