The distribution characteristics of cotton roots(Gossypium hirsutum L) in different irrigation amounts were investigated by digging in this study.The result indicates that: with depth increased,root biomass gradually decreased in different irrigation amounts.But there is an increased trend in deep-seated root biomasses only with irrigation amount decreased.Underground biomass has a significant negative logarithm relation with soil depth in different irrigation amount.Root length and root surface area have the same changeable rule.In every irrigation amount treatment,with depth increased,root length and root surface area change as a single peak curve with the increase of soil depth.Root extinction coefficient of cotton in different irrigation amounts was calculated by SigmaPlot.The result indicates: with irrigation amount decreased,root extinction coefficient of cotton shows an increased trend.