The Aβ1-42 zebrafish model, established via intracerebroventricular microinjection, was employed to investigate the ameliorative effects of Pseudostellaria heterophylla fractionated polysaccharides (PF30, PF60, PF90) on Alzheimer's disease (AD)-associated cognitive deficits, as well as the underlying mechanisms and the primary active constituents responsible for these effects. The total sugar, protein content and molecular weight of PF30, PF60 and PF90 were determined by phenol-sulfuric acid method, Coomassie brilliant blue method and gel chromatography, respectively. UV and FT-IR spectroscopy were sued for characterization. Novel object recognition, reward T-maze behavior experiments were performed to explore the effects of PF30, PF60, and PF90 on cognitive impairment in the AD zebrafish model. Fluorescence quantitative PCR was used to determine the expression levels of related mRNAs in the zebrafish brain. The results revealed that the mass fractions of total sugar contents of PF30, PF60 and PF90 were 70.54%, 69.00% and 80.19%, respectively; the mass fractions of protein contents were 2.51%, 5.08% and 1.89%, respectively; the molecular weights (Mw) were 23.1, 8.97 and 1.72 ku, respectively. The comparison of the results of zebrafish experiments revealed that PF30 significantly increased the retention time of zebrafish in the new arm and the reward arm, increased the number of times the zebrafish entered the new arm and the reward arm, alleviated the brain neuroinflammation, significantly inhibited the expression of CDK5 and GSK-3β, and ameliorated the cognitive memory impairment in zebrafish. Therefore, PF30 showed the greatest ameliorating effect on cognitive impairment in zebrafish among the three graded polysaccharides of Pseudostellaria heterophylla.