To investigate the effects of carbonate alkalinity stress on the tissue structure and osmoregulatory gene expression of the oriental river prawn （Macrobrachium nipponense）， juvenile M. nipponense （3.12±0.42）g were subjected to an acute carbonate alkalinity stress experiment to determine the 96-hour lethal concentration （LC₅₀）. Based on this， the control group （1.5 mmol/L） and the carbonate alkalinity treatment group （10 mmol/L） were set up with triplicate to carry out the acute stress test of carbonate alkalinity for 96 h. The results showed that the 96-hour LC₅₀ value for juvenile M. nipponense under carbonate alkalinity stress was 16.89 mmol/L， with a safe concentration at 6.47 mmol/L. In contrast to the control group， with the extension time of carbonate alkalinity stress， the gill epithelial cells and columnar cells in the experimental group were arranged disorderly， and the secondary lamellae began to swell. In hepatopancreas of M. nipponense under carbonate alkalinity stress， the volume of B cell internal running vesicles increased， and the boundary between some hepatopancreas tubules was blurred. Compared to control group， the height of intestinal mucosa and muscle thickness of juvenile prawn obviously decreased in intestine of M. nipponense under carbonate alkalinity stress， and structural integrity of intestinal microvilli in juvenile prawns was deteriorated with the increasing time of carbonate alkalinity stress. It was found that the gene expression of carbonic anhydrase 3 （CA3） and Na⁺-K⁺ exchanging ATPase （NaK-ATP） in the gill tissues of prawn in carbonate alkalinity treatment group were significantly higher （P<0.01） than that of the control group within 96 h. The gene expressions of CA3 and NaK-ATP in the hepatopancreas of prawn in carbonate alkalinity treatment group were significantly higher （P<0.01） than those in the control group within 24 h， but there was no significant difference between the control group and carbonate alkalinity stress group along with coercion time extension. The present study shows that high carbonate alkalinity stress can affects the gill， hepatopancreas and intestinal histology of juvenile prawns， and the osmotic pressure regulating gene expression pattern shows a trend of first increasing and then decreasing. This study can provide reference data for large-scale culture of M. nipponense juveniles in salt-alkali water.