Abstract: A pot experiment was carried out to test the effects of phosphorus (P) supply levels (25, 50, and 75 mg P₂O₅·kg^-1) with two P genotype (efficient DH110+ and DH147, inefficient DH49) barleys on root morphology and the relationships between root morphology and P uptake. The results showed that barley biomass and P uptake were significantly reduced by low P stress. Efficient genotype barley biomass and P uptake were 1.24-1.70 and 1.18-1.83 times as much as those of inefficient genotype barley respectively. The total root length, total root surface area, average root diameter, adventitious root length and root surface area, lateral root length and root surface area of P efficient genotype barley were significantly reduced with decreasing the P supply level in soil. The total root length, total root surface area, specific root length, lateral root length and surface area of P efficient genotype barley were 1.46-2.06, 1.12-1.51, 1.35-1.72, 1.69-2.42, and 1.40-1.78 times as much as that of those of P inefficient genotype barley, respectively, while the average root diameter was 70.6%-90.2% of P inefficient genotype barley. Principal component analysis showed that the average root diameter, specific root surface area and specific root length could be used to distinguish two P genotype barleys. Partial least squares regression analysis showed that the total root length, total root surface area made great contributions to P uptake of barley in soil. The contribution of the adventitious root length and surface area on P uptake of barley decreased significantly and the average root diameter, specific root length, lateral root length and root surface area increased with the decreasing P supply level in soil. P efficient genotype barley adapted to low P stress through maintaining the lateral root growth, increasing the specific root length and root fineness.