[Objective] To investigate the influence of plant endophytic fungus Piriformospora indica on the model legume Medicago truncatula. [Methods] Root length, root and shoot fresh weight were recorded under the P. indica colonization. Antioxidant enzyme activities were analyzed with special focus on superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). The proline content was determined by acidic ninhydrin method, and betaine aldehyde dehydrogenase gene (BADH) expression was semi-quantitative identified by RT-PCR. [Results] Root colonization by P. indica increased plant growth and attenuated the NaCl-induced growth inhibition. The endophyte significantly increased antioxidant enzyme activities and proline content. Additionally, P. indica induced the BADH expression under salt treatment. [Conclusion] The experiment data revealed the potential of P. indica in application as a plant growth-promoting mycorrhizal fungus for realizing the salty-soil improvement indirectly.