The swimming crab (Portunus trituberculatus) is a commercially important marine crab in China. It is distributed in China, Japan and Korea and has the largest production in the Yellow Sea and Bohai Sea. It has the characteristics of fast growth, high edible value, breeding profit, etc. Salinity is closely related with osmoregulation of aquatic crustacean animal. Adaptation of aquatic crustacean animal to the changes of the salinity is mainly controlled by the osmotic pressure of the blood. The osmotic pressure level of the aquatic crustacean animal is mainly determined by the content of the inorganic ions and free amino acids in the blood. In addition, it is also affected by the metabolism of carbohydrate, lipid, protein, ammonia and other substances in the blood. In order to investigate the change regulation and characteristics of serum biochemical indicators of “Huangxuan No.1” P. trituberculatus during salinity stress, four salinity gradients (salinity 5, 10, 20, 50) experimental groups and a control group of salinity 30 were set up in the experiment. The samples of the experimental groups were respectively taken at 3, 6, 9, 12, 24, 48, 72 h and the samples of the control group were taken at 0, 3, 6, 9, 12, 24, 48, 72 h. The results showed that the values of serum glucose (GLU), triglyceride (TG) and total protein (TP) of the experimental groups declined firstly and then became stable, and were significantly lower than the control group. The values of serum GLU, TG and TP of the control group were stable during 0-72 h. While the contents of serum GLU, TG and TP of the experimental group were stable, the larger difference of the salinity between experimental and control group, the greater decline of the contents of serum GLU, TG and TP. Maximum decline of serum GLU and TP content was greater than the maximum decline of serum TG content. The values of serum GLU of experimental groups declined quickly during 0-9 h. The values of serum TG and TP declined during 0-12 h. The maximum decline of the value of serum TP was less than the maximum decline of the value of serum GLU in salinity 20 experimental group. The maximum decline of the value of serum TP was greater than the maximum decline of the value of serum GLU in salinity 5, 10, 50 experimental groups. The values of serum urea(UREA) of the experimental groups rose firstly and then became stable, and were significantly higher than the control group. The value of serum UREA of salinity 5 experimental group was near the value of serum UREA of salinity 50 experimental group. However, the values of serum TP of salinity 10 and 50 experimental groups were near each other. It could be concluded that GLU, TP and TG in serum of P. trituberculatus were closely related to osmoregulation. Serum GLU and TP of P. trituberculatus were main materials for energy supply and the serum GLU supplied energy firstly in the osmoregulation process. Partial content increase of serum free amino acid of P. trituberculatus could be derived from other tissues in high salt water environment.