Abstract: 【Objective】 To study the effects of agronomical character and leaf photosynthetic parameters by different concentrations of glyphosate on glyphosate island cotton in the hope of providing chemical skills for weeding. 【Methods】 Using glyphosate-resistant Xinchangmian 5 as the research object and spraying four concentrations of glyphosate1.25%, 2.5%, 5.0%, 10.0% at 10 leaf stage, respectively, then plant height, stem diameter, leaf stage and photosynthetic indexes were measured. 【Results】 Compared with the control, plant height, stem diameter, leaf stage, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum photochemical efficiency of PSⅡ(Fv/Fm) and potential activity of PSⅡ(Fv/Fo) with treated by four concentrations of glyphosate were all decreased in sea island cotton. The glyphosate with higher concentrations, the more dramatic decline. However, the intercellular CO₂ concentration (Ci) showed an increasing trend. The treatment by 1.25% and 2.5% had no difference with control after 14 days of spraying, and the agronomic traits returned to the normal level after 24 days. 【Conclusion】 The growth trends reduce significantly by spraying 4 concentrations of glyphosate at the bud stage. More than 5% concentration of glyphosate affect the growth seriously sea island cotton Xinchangmian 5, so it is suggested that concentration below 2.5% of glyphosate be applied in production.