Abstract: Using Hemerocallis as the experimental object, the effects of photosynthetic rate, chlorophyll content and root vitality of Hemerocallis treated with quizalofop-p-ethyl of 400, 800, and 1200 mg/kg were studied. Results showed that there was no significant difference between the treatment and control group in terms of the photosynthetic rate, chlorophyll content and root vitality of Hemerocallis after treatment at the same time. After treatment with quizalofop-p-ethyl, the photosynthetic rate, chlorophyll content, and root vitality of Hemerocallis showed significant time effects. Two-way ANOVA showed that the photosynthetic rate of Hemerocallis on the 6th and 10th day was significantly higher than that on the 13th and 17th days after treatment; On the 6th day after the treatment, the photosynthetic rate of Hemerocallis was the highest, with CO₂ reaching at the 9.9417 mg·cm^–2·h^–1, which was significantly higher than that on the 13th day by 287.48% after treatment; The contents of chlorophyll a, chlorophyll b and total chlorophyll were the highest value on the 8th day after treatment, and then showed the decreasing trend with the extension of time; And the root vitality of Hemerocallis reached the peak on the 10th day after treatment., which was significantly higher than that on the 6th and 13th days after the treatment by 136.67% and 77.11%, respectively. The research results can provide a theoretical basis for the application of quizalofop-p-ethyl in the field of Hemerocallis.