Abstract: In order to select high nitrogen-fixing azotobacter strains, nitrogenase activity of 13 strains separated in the rhizosphere in Gansu non-leguminous crop fields were measured by acetylene reduction method. Also the fertilization effect of the strains on spring wheat was investigated via pot experiment. The results show some degree of promotion effects of 13 azotobacter strains on spring wheat grain yield, biomass and the yield components. N6, N10, N13, N14, N27 and N42 strains presenting relative stronger promoting effects on spring wheat yield have application prospects as the bacteria strains of microbial fertilizer. N13 strain significantly increases spring wheat yield. The grain yield, biomass, panicle weight, panicle grain number, 1000-grain weight, plant height and panicle length with N13 respectively increase by 66.04%, 54.19%, 47.65%, 37.91%, 20.42%, 5.16% and 21.89% compared to the treatment with similar fertilizer amount. Its nitrogen-fixing amount in spring wheat soil is 212.55 mg per pot, and nitrogenase activity is significantly higher than other strains, reaching 139.79 nmol (C₂H₄)·h^-1·mL^-1.