To investigate the impact of microcrystalline aluminum hydroxide gel（AH₃） content on the properties of high-alkali carboaluminate cementitious materials， a composite activation scheme was designed using a co-mixed solution of sodium hydroxide， aluminum hydroxide and a sodium aluminate solution， to activate limestone powder. The results indicate that as the proportion of sodium aluminate solution in the activator mixture increases from 0% to 100%， the content of monocarboaluminate in the matrix remains relatively stable， while the content of microcrystalline AH₃ progressively increases and the content of gibbsite correspondingly decreases. The average crystallite size of microcrystalline AH₃ is approximately 19.5 nm， which is significantly smaller than the median particle size of 5.82 μm for gibbsite， thus endowing it with a larger specific surface area and superior cementitious properties. With the increase of microcrystalline AH₃ content， the proportion of gel pores in the matrix increases， resulting in a more compact pore structure. Furthermore， there is a linear positive correlation between compressive strength of samples and the content of microcrystalline AH₃， suggesting that higher content of microcrystalline AH₃ correlates with greater strength of samples.