The experiment was conducted to investigate effects of different P levels(P1 0.1 mmol/L,P2 5 mmol/L)on root morphology and characteristics of rhizosphere in different Pefficiency cotton under the gravel culture conditions.Two different Pefficient cotton genotypes(the P efficient ZM42 and the P inefficient XLZ13)were selected for the study.Crop biomass,P uptake amount,root morphology,available P,pH and phosphatase activity in the rhizosphere were measured.Result showed that under the sand culture cotton biomass and accumulation of phosphorus increased with phosphorus application for both the Pefficient genotypes cotton.Root biomass,P uptake and root to shoot ratio of ZM42 was better than XLZ13.length of fine root(0~0.4 mm)in ZM42 was looger than XLZ13,and the proportion of fine roots in the total root length was higher,which was helpful to promote phosphorus absorption of plant.When the phosphorus content in growth medium was lower,to reduce the pH in the cotton rhizosphere also decreased.The pH of the rhizosphere of ZM42 was significantly higher than XLZ13.Rhizosphere phosphatase activity of two kinds of phosphorus efficiency cotton was increased as the phosphorus content decreased in the two periods.Phosphatase activity of ZM42 was higher than that of XLZ13.Thus,there was a difference with rhizosphere mechanism between the two phosphorus efficiency of cotton in the same growth medium,the change of root morphology characteristic of the P efficient cotton was one of the main mechanisms of rhizosphere phosphorus activation.