Abstract: To study the effect of saline-alkali stress on dry mass, rhizosphere soil enzyme activities and soil microbial quantities, pot experiments were designed two sugar beet varieties, ‘KWS0143’ (strong tolerance to saline-alkali) and ‘Beta464’ (weak tolerance to saline-alkali) planted in different Na₂CO₃ concentrations [0% (control), 0.4%, 0.8% and 1.2% of soil], and the dry mass of seedlings,soil enzyme activities and amount of microbiology in soil were recorded. The results showed that compared with the control, the dry mass of seedlings was significantly increased in the treatment of 0.4% Na₂CO₃, while it was significantly decreased in the 0.8% and 1.2% Na₂CO₃ treatments. Significant differences among treatments were observed. The soil urease, alkali phosphatase and peroxidase activities in the root rhizosphere of seedlings presented a similar tendency under different concentrations of Na₂CO₃. Compared with the control, the enzyme activities with the treatment 0.4% Na₂CO₃ were not significantly enhanced, while those in the treatment of 0.8% and 1.2% Na₂CO₃ were significantly reduced. All the soil enzymes’ activities in ‘KWS0143 were higher than in ‘Beta464’. The 0.4% Na₂CO₃ did not lead to significant change of soil microbial community, but 0.8% and 1.2% Na₂CO₃ sharply decreased the amount of soil bacteria, fungi and actinomycets (P<0.05). The amount of rhizosphere soil microbe in ‘KWS0143’ was higher than in ‘Beta464’. There were significantly positive correlation among the dry mass, soil enzymes and soil microbe of the two varietie. Path coefficient analysis showed the determinant coefficient of ‘KWS0143’ dry mass was in order of sctinomycetes > bacteria > peroxidase > urease > fungi > alkali phosphatase, while that ‘Beta464’ dry mass was in order of actinomycetes > peroxidase > urease > fungi > alkali phosphatase > bacteria.