Abstract: In order to improve the number of nodules and yield of native alfalfa, and establish a high efficient symbiosis between alfalfa and Sinorhizobium meliloti, the obtained SD101 was identified as a strain of Sinorhizobium meliloti by using 16S rDNA sequencing method. Pot experiments were conducted to study the nodule numbers and heights of‘Aohan’and‘Longmu 801’in different medium treatments after inoculating SD101 and protective agent. Field trials were conducted to study the nodule numbers and yields of‘Aohan’ and‘Longmu801’after inoculating SD101 and protective agent. It was found that‘Aohan’and‘Longmu801’ had high numbers of nodules and yields by inoculating SD101 and protective agent, and were significantly different compared with the treatments without inoculating SD101. The results showed that implementing urea could inhibit the growth of nodules and the symbiosis of alfalfa and SD101 to a certain extent. Soil samples could be completely sterilized by γ ray. In the field trials, native rhizobium played an important role in the growth of alfalfa, but the seed dressing with Sinorhizobium meliloti SD101 and protective agent was more competitive.