Abstract: As a cold-blooded animal,fish is particularly sensitive to the changes of the water temperature,and makes rapid response in physiological changes at the same time.This study analyzed the variation law of serum cortisol,blood glucose and lactic acid in the juveniles of large yellow croaker under the stress of mutation high temperature.To make it clear,the experiment selected large yellow croaker,the average weight was(118.8±6.05) g and 8-month-old as experiment object,and maintained the temperature at (23±0.3)℃(the control group) and(33±0.3)℃(the test group),temperature-changing process was mutation,then we observed and recorded the experimental phenomena.The results indicated that the juveniles of large yellow croaker had a strong stress response,such as accelerating breathing,extreme anxiety,intense swimming, when subjected to high temperature stress at 33℃.The serum of the test group showed a significant increase in cortisol,glucose,lactic acid content compared to the control group(P<0.05 or 0.01) after two hours,and then the juvenile of test group started to die in succession,eventually all died.Research showed that the high temperature of 33℃ stress had a fatal effect on the large yellow croakers,and we should strictly control the water temperature below 33℃ in the actual production.