[Background] Algae, bacteria and their interspecies interactions play important roles in aquatic ecosystem. In recent years, salinization of some rivers, lakes and other freshwater resources has become more serious, which greatly impacts the aquatic ecosystem. However, how salt stress influences the algae-bacteria interaction and whether certain bacteria can enhance algal salt tolerance remain unclear. [Objective] To isolate and identify the bacteria that can promote the salt tolerance of freshwater alga, Chlamydomonas reinhardtii, and analyze the relevant mechanism. [Methods] Effective bacteria were screened through enrichment culture, isolation and co-culture experiments. The algal growth ability under different conditions was assessed based on cell concentration, chlorophyll content and other parameters. In addition, 16S rRNA gene sequence analysis and genome sequence analysis were carried out to predict the possible mechanism of algae-bacteria interaction. [Results] A bacterial strain, MEZX29, was isolated, which could significantly enhance the salt tolerance of C. reinhardtii under the condition of 250-290 mmol/L NaCl. The 16S rRNA gene sequence analysis indicated that MEZX29 might belong to Rhodococcus qingshengii. The genome sequence analysis showed that MEZX29 contained the genes involved in glucose metabolism, ethylene metabolism, and biofilm formation, which might play roles in this salt tolerance enhancement. [Conclusion] R. qingshengii strain MEZX29 could enhance the salt tolerance of C. reinhardtii, which provided a new material for studying the beneficial interaction between algae and microorganisms.