The swimming crab Portunus trituberculatus is an important fishery and aquaculture species in China, and salinity has a significant effect on its physiological processes. To verify whether the calcyclin-binding protein (CacyBP) gene is related to salinity stress adaptation, a cDNA fragment of P. trituberculatus CacyBP was amplified and cloned. The cloned PtCacyBP fragment contains 702 nucleotides encoding 233 amino acids, with a calculated molecular weight of 26.35 kDa. PtCacyBP has approximately 40% amino acid sequence identity with homologs from other known species. To further validate the salinity tolerance roles of PtCacyBP. this study investigated the prokaryotic and eukaryotic expression of a PtCacyBP recombinant plasmid under a series of salinity stresses. A recombinant pET28( )-PtCacyBP prokaryotic expression plasmid was constructed and expressed in Escherichia coli DE3 (BL21). Moreover, an EGFP-C2-PtCacyBP eukaryotic expression plasmid was constructed and transfected into 293T cells, which were grown under a series of salinity stresses. During these salinity challenges, the survival of both prokaryotic and eukaryotic cells with the recombinant plasmid was significantly higher than the survival of cells that contained the plasmid without an insert. Therefore, the results indicate that PtCacyBP confers a protective effect against salinity stress and may be involved in the physiological process of salinity adaptation in P. trituberculatus.