In order to improve and utilize saline-alkalinesoil，saline -alkali soil from Daqing grassland was selected asthematerial，and the saline -alkali tolerant bacteria were separated byscreening，then 16S rRNA gene was applied topreliminarily and taxonomically classify thestrain，and the ability for nitrogen -fixation wasanalyzed.Two treatments were setup to study alfalfa seeds germination(CK1:sterile distilledwater；S1:adding bacterialinoculant)to compare the differentof the seeds germinationrate，seedlinglength，and freshweight.Another two treatments(CK2:sterile distilledwater；S2:adding bacterialinoculant)were conducted to analyze the growth characteristics and antioxidative activity of alfalfa under NaHCO3stress.The results showed that a total of 43 strains wereisolated； one strain designated as S38 was classified into the genus of Planococcusbased on 16S rRNA genesequence，and it showed to have the abilities of nitrogen -fixation and ACC-deaminase-activity.Compared S1 withCK1，the alfalfa inoculated by S38 significantly increased the germinationrate，seedling length and fresh weight.Compared S2 withCK2，the biomass of overground and underground of the alfalfa inoculated by S38 under NaHCO3stress increased by 32% and50%，respectively，theChla，Chlb and Chla+Chlb contentincreased by1.33，1.15 and 1.28times，respectively，but the soluble sugar content and antioxidant enzymes(SOD，POD，CAT)activityreduced，and absorption and distribution of the K +decreased.It follows that S38 has a promoting effect onalfalfa seeds germination and the seedings growthmorphology，root morphology and photosynthesis under saline -alkalistress，and reduces the absorption of salt byalfalfa，thereby promotes the growth ofseedlings.Insummary，S38 plays an importantrole in alleviating growth damage of plant under alkalistress.