In this study, the toxic mechanism of Procambarus clarkii responding to high pH stress was investigated through analyzing the effect of high pH on enzymes activity and histological structure of gill and hepatopancreas. Based on the 96 hours median lethal concentration, Procambarus clarkii were exposed to two pH levels:pH 7.6 (control group) and pH 10.2 (experimental group). Each group was respectively sampled for measuring activity of Na⁺-K⁺-ATPase, lactate dehydrogenase (LDH), fumarate reductase (FRD) in gill, measuring activity of superoxide dismutase (SOD), catalase(CAT) and content of malondialdehyde (MDA) in hepatopancreas, and observing the histological structure of gill and hepatopancreas at 0, 2, 8, 24, 96 h. The results showed that the value of pH LC₅₀ was 10.194 at 96h. Activity of gill Na⁺-K⁺-ATPase, LDH, FRD in experimental group presented the trend of rising and were significantly higher than those in control group(P<0.05) after 8 h exposure. With pH stress time prolonging, the variation trend of malondialdehyde content in experimental group was similar to LDH and FRD. Activity of hepatopancreas CAT in experimental group presented the trend of rising firstly and declining afterward. Activity of hepatopancreas SOD was decreased significantly(P<0.05) after 24 h exposure. Procambarus clarkii exposed to high pH displayed histological alterations in the gill and hepatopancreas. Gill tissues showed respiratory epithelium cells were exfoliated gradually, and cuticle rupture. The hepatopancreas indicated basement membranes of hepatopancreas tubule were ruptured, the enlarged size and increased number of vacuoles in hepatopancreas tubule, and the number of hepatocytes was decreased distinctly. The results indicated that high pH stress will affect the metabolism of Procambarus clarkii and will arouse oxidative stress, The histological structure of gill and hepatopancreas will also be affected by high pH stress, as well as their biological functions.