This study examined the effect of low-pH stress on physiological metabolism and the histological structure of gill and hepatopancreas in with the body weight of (25.88±4.40) g, using paraffin section technology and the measurement of biological enzyme activity. Based on the 96 h median lethal concentration (LC₅₀), water for 96 h. A control group of the species was also exposed to water of pH 7.6. Each pH level was sampled to measure the activity of metabolic enzymes in the gill and antioxidant properties in the hepatopancreas, and the histological structure of gill and hepatopancreas was observed at 0 h, 2 h, 8 h, 24 h and 96 h. The results showed that the value of pH LC₅₀ was 3.675 at 96 h. The activity of Na⁺-K⁺-ATPase and lactate dehydrogenase (LDH) in gills of the experimental group gradually increased, while activity of cytochrome oxidase (COO) in the gill showed the opposite trend after low-pH stress. As pH stress time was prolonged, the activity of hepatopancreas superoxide dismutase (SOD) and catalase (CAT) in the experimental group increased at first, then declined. The MDA content in the experimental group increased consistently during the exposure time (P. clarkii exposed to low-pH water (pH 3.6) showed impairment of cuticle and exfoliation of respiratory epithelium cells. Observation of hepatopancreas microstructure sampled from exposed to low-pH water (pH 3.6) indicated the appearance of more B cells and inter-transferred vacuoles in the hepatopancreas tubules, which were enlarged. I am not sure I have understood your intention correctly, so please check carefully. It also showed that the number of granular materials in the transferred vacuoles hadincreased and that the structure of the hepatopancreas tubules was impaired. The study indicated that low-pH stress will affect the physiological metabolism and lead to hypoxia. Antioxidant activities by will be induced by short-term pH stress but inhibited when exposure time is prolonged. Low-pH stress will damage the structure of both gill and hepatopancreas.