Objective: To evaluate and analyze the effect of underwater Tai Chi on lower limb motor function in patients with hemiplegia after stroke. Methods: A total of 40 patients with hemiplegia after stroke admitted to the Rehabilitation Center of Wudang Mountain Hospital of Taihe Hospital from September 2021 to June 2022 were selected and divided into study group and control group by random number table method, with 20 cases in each group. The control group received routine rehabilitation treatment, and the research group also received water tai chi therapy on this basis. After 8 weeks of treatment, the improvement of neurological function, lower extremity function and ability of daily living were evaluated and compared between the two groups. Result: After 8 weeks of treatment, the total effective rate of neurological function improvement in the study group was higher than that in the control group, the difference was statistically significant (P > 0.05). After 8 weeks of treatment, the scores of the FMA-LE scale and MBI scale of patients in both groups were increased, and the difference was statistically significant compared with before treatment (P < 0.05). The scores of FMA-LE scale and MBI scale in the study group were higher than those in the control group, and the difference was statistically significant (P < 0.05). Conclusion: Water Tai Chi training for patients with hemiplegia after stroke can promote the improvement of nerve function, lower limb function and ability of daily living.