In the previous studies，the global transcriptome databases of Mesorhizobium huakuii 7653R in free living and in symbiotic condition were constructed respectively. Some differential expression genes in free living and symbiotic condition were identified with RNA-Seq and Microarray. Among these genes，MCHK_7135 belongs to the peroxiredoxin （Prxs） family. Its expression was significantly up-regulated at the stage of symbiotic nitrogen fixation.In this article，the replacement mutants and complementary strains of MCHK_7135 were constructed by homologous recombination to study the function of MCHK_7135 gene in symbiotic nitrogen fixation between rhizobia and host plants. The phenotypes of mutant and complementary strains were investigated under free living and symbiotic condition with Astragalus sinicus. Results showed that the mutant strain of MCHK_7135 gene was more sensitive to H₂O₂ stress compare with the wild-type strain. The growth of A. sinicus plant inoculated with the mutant was inhibited，the number of infect thread and nodule primordia decreased，the number of nodule was small，and the activity of nitrogenase was low. However，when the mutant strain was complemented by complete MCHK_7135 gene，some symbiotic phenotypes were restored to different degree. It is indicated that the peroxiredoxin gene MCHK_7135 of M. huakuii plays an important role in the symbiotic nitrogen fixation between rhizobia and host plants.