Abstract: A nutrient solution experiment was conducted to investigate the effect of different levels of phosphorus supply on root morphology and root-water-uptake characteristics of soybean seedlings. Phosphorus concentration had less effect on root dry weight than on shoot dry weight. Low phosphorus stress increased root dry weight and root/shoot ratio. Phosphorus concentration has significant effect on root morphology of soybean seedlings. Root length,root surface area and root volume initially decreased and then increased with increasing phosphorus concentration. The proportion of root length within 0~1 mm diameter was 93%. Daily average root-water-uptake rates per plant increased with increasing phosphorus concentration within 0~30 μmol·L^-1,but decreased when phosphorus concentration was over 30 μmol·L^-1. Thus,the soybean roots would change their root morphology in response to various phosphorus concentrations to some extent. In other words,soybean roots would increase under low phosphorus condition but decrease under high phosphorus condition.