There are superior performance and broad application prospects for acid-activated geopolymer, while its popularization and application are hindered because of the potential drying shrinkage problem. Bentonite was adopted to modify acid-activated geopolymers. Influences of acid concentration and bentonite content on the mechanical properties, length change rate, water loss and microstructure in dry environment were analyzed to provide guidance for solving the problem of geopolymers drying shrinkage. Results show that under different bentonite content, the higher the acid concentrations, the greater the apparent density, while the compressive strength and specific strength of specimens is increased first and then decreased. The peak strength and apparent density of specimens show a decreasing trend as the increase of bentonite content. With the development of age, the length change rate of specimens increases gradually and tends to be balanced. In the weak acid environment, the higher the bentonite content, the smaller the length change rate of specimens, which is consistent with the daily mass loss of specimens. The total porosity of specimens with different bentonite contents decrease first and then increase with the increase of acid concentration. When the acid concentration is the same, the total porosity of the specimen increases with the increase of bentonite content.