Sterile seedlings of Potamogeton crispus were cultured by tissue culture technique which was used as experimental material. In this study, we investigated contents of element, photosynthetic pigments, reactive oxygen species(ROS), malondialdehyde (MDA) and proline(Pro), polyamines(PAs) as well as activities of antioxidant enzymes in Cr⁶⁺-treated P. crispus under different pH values so as to approach the physiological and biochemical mechanisms of pH value in affecting Cr⁶⁺ toxicity of aquatic plants. The results indicated that, (1) Acidic conditions enhanced the accumulation of Cr while pH 7.0 treatment helped P. crispus maintain the balance of nutrient elements; (2) pH 6.0, 7.0 and 8.0 treatments could retard the chlorosis and promote the biosynthesis of photosynthetic pigments; (3) Contents of ROS and MDA increased when the pH was 4.0, 5.0 and 9.0. Activities of superoxide dismutase and catalase were improved when the pH value was 4.0 and 5.0; However, activity of peroxides decreased with the increase of pH value; (4) In response to Cr⁶⁺ stress, plants showed sharp increase in proine content when the pH was 6.0 and 7.0; (5) An improved level of putrescine(Put) was noted in pH 4.0 and 5.0 treatments while spermidine(Spd) and free (Spd + Spm)/Put ratio increased in pH 6.0 and 7.0 treatments; For spermine(Spm) content, it generally increased with pH value and it was lower of the pH 4.0 and 5.0 treatments than that of the control group. Our results demonstrated that resistance of P. crispus to Cr⁶⁺ stress could be enhanced by reducing the excessive accumulation of Cr, promoting photosynthetic pigments, removing ROS efficiently, maintaining the balance of nutrient elements and keeping high levels of Pro, PAs as well as free (Spd + Spm)/Put ratio when pH value was within the range of 6.0-7.0.