Heat shock protein 90 is a multi-functional molecular chaperone that plays an essential role in both cellular metabolism and stress response. The swimming crab, Portunus trituberculatus is an important marine fishery and aquaculture species. Water salinity conditions influence its artificial propagations significantly. In order to prove the relationships between HSP90a protein and salinity stress, we investigated the prokaryotic expression of P. trituberculatus HSP90a recombinant protein under a series of salinity stress. Based on the coding sequences of P. trituberculatus HSP90a protein in GenBank, we cloned the full length of HSP90a gene. Recombinant pET28-HSP90a prokaryotic expression recombinant plasmid was constructed and expressed in Escherichia coli. DE3 (BL21) under a series of salinity stress. Results showed that the survival rate of recombinant plasmid transferred Escherichia coli was higher than that of empty vector transferred cells. When the salinity challenge was close to the salinity tolerance maximum value of E. coli, the difference of survival rate between those two kinds of cells became more significant. For example, at the highest salinity challenge condition (1 050 mmol/L), the survival rate of recombinant plasmid transferred E. coli was 10.7 times higher than that of empty vector transferred cells. Therefore, our results indicated that P. trituberculatus HSP90a protein possessed protective effect against salinity stress and HSP90a protein might be involved in salinity adaptation physiological process in P. trituberculatus.