Based on the bioinformatics prediction of small non-coding RNA(sRNA), SraG sRNA was predicted and confirmed by Northern blotting. The full-lengh SraG was obtained with RACE and high-throughput sequencing of transcriptome. The secondary structure and target genes of SraG were predicted with RNAfold and TargetRNA software,respectively. To confirm the function of the SraG gene in symbiotic nitrogen fixation, a disruptant strain of SraG was constructed and named M. huakuii SraGmut. The pot experiments of plant nodulation were conducted to examine the nitrogen fixation ability of the disruptant strain. The nitrogenase activity of A. sinicus L. inoculated M. huakuii SraGmut was only 40% of that of inoculated M. huakuii 7653R, indicating that SraG as a RNA affected the symbiotic nitrogen ability of the rhizobium tested. It provides a solid foundation for studying the functional mechanism of sRNA during symbiotic nitrogen fixation of rhizobium in the future.