The use of various solid wastes to prepare geopolymers can promote the engineering application of low-carbon cementitious material and the recycling of solid waste resources. This study used air-cooled nickel slag with low reactivity as the main precursor and incorporated ground granulated blast furnace slag to prepare geopolymers. The influence of ground granulated blast furnace slag content and alkali activator modulus on autogenous shrinkage and drying shrinkage were investigated. The pore structure of the hardened body was characterized by the nitrogen adsorption method, and the relationship between shrinkage performance and pore structure was explored. The results show that the increased ground granulated blast furnace slag content enhances the compressive strengths of geopolymers, and meanwhile reduces the autogenous shrinkage. The formation of calcium alumino silicate hydrate (C-A-S-H) gel phase fills into the pores in geopolymer to reduce the overall pore volume. This is helpful in constraining the capillary pore water loss under drying conditions, and consequently the drying shrinkage is mitigated. The increased alkali activator modulus enhances the capillary pore volume. The development of higher capillary pressure due to self-desiccation and water evaporation on drying results in both higher autogenous shrinkage and drying shrinkage.