Abstract: Hydroponic experiments were conducted in a growth chamber and changes in the hydraulic conductivity of sorghum (Sorghum vulgare Pers.) roots (Lpr) at the three‐leaf stage were measured using the pressure chamber method. Water deficiency was imposed with polyethylene glycol (PEG) 6000 and the phosphorus (P) levels were controlled by complete Hoagland solution with and without P nutrient. The objective of this study was to investigate the effect of P nutrition on root Lpr under water deficiency. The results showed that the Lpr in P deficiency treatments decreased markedly, but the Lpr recovered to the same value as that of control when sufficient P was supplied for 4–24 h. Water deficiency decreased Lpr, but the hydraulic conductivity of the roots with sufficient P supply was still higher than that of plants without P supply. When resuming water supply, the Lpr of the water‐deficient plants under P supply recovered faster than that of plants without P supply, which indicates that plants with sufficient P nutrient are more drought tolerant and have a greater ability to recover after drought. The treatment of HgCl2 indicated that P nutrient could regulate the Lpr by affecting the activity and the expression levels of aquaporins.