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Abstract: 【Objective】Explore the effects of different gradients of microbial fertilizer application rate on sugar beet yield and quality in saline-alkali land in the Yellow River Irrigation Area,to find out the optimal sugar beet microbial fertilizer application rate in saline-alkali land.【Methods】In Bayannur City,Inner Mongolia,from 2020 to 2021,five microbial fertilizer application treatments,including T1（0 kg/hm²）,T2（75 kg/hm²）,T3（150 kg/hm²）,T4（225 kg/hm²）and T5（300 kg/hm²）were set up on the basis of two main cultivation modes of flat cropping and ridge cropping. The effects of different treatments on sugar beet yield and sugar yield were analyzed. Based on the variation law of sugar beet yield and sugar yield,a regression model with the application rate of microbial fertilizer was established. And the optimal application rate of microbial fertilizer was calculated. The accuracy of the model was tested by normalized root mean square error（NRMSE）and 1∶1 histogram between the measured value and the estimated value.【Results】The application of microbial fertilizer in saline-alkali land of the Yellow River Irrigation Area significantly improved sugar beet yield and sugar yield. In 2020,T3 treatment had the highest sugar beet yields both in flat cropping and ridge cropping at 71 454 and 73 835 kg/hm²,respectively,increased by 24.53% and 20.37% compared to T1 treatment. In 2021,T5 treatment had the highest sugar beet yields of 67 934 and 70 863 kg/hm²,respectively,increased by 14.55% and 12.54% compared to T1 treatment. In 2020,T3 treatment had the highest the sugar yields of 11 737 and 12 314 kg/hm² in flat cropping and ridge cropping respectively,increased by 30.93% and 24.68% compared to T1 treatment. In 2021,T5 treatment had the highest sugar yields of 10 836 and 11 374 kg/hm² respectively,increased by 17.50% and 13.06% compared to T1 treatment. Under the flat cropping and ridge cropping modes,the models of sugar beet yield and microbial fertilizer application rate were y=-0.224 6x²+96.845x+58 126,R²=0.817**;y=-0.207 8x²+88.685x+62 334,R²=0.723**. The models of sugar yield and microbial fertilizer application rate were y=-0.049 8x²+20.112x+9 036.4,R²=0.806**;y=-0.045x²+18.215x+9 929,R²=0.714**. Based on the above models,it was calculated that the maximum yields of 68 568 and 71 796 kg/hm² can be achieved by applying microbial fertilizer of 215.6 and 213.4 kg/hm² in flat cropping and ridge cropping mode. The maximum sugar yield of 11 067 and 11 772 kg/hm² could be achieved when microbial fertilizer was applied at 201.9 and 202.4 kg/hm² respectively. The model tests showed that the linear relationship between the measured and estimated sugar beet yields,as well as the measured and estimated sugar yields,all had extremely significant correlations,indicating good accuracy of the models.【Conclusion】The application of microbial fertilizer in saline-alkali land of the Yellow River Irrigation Area significantly improved the yield and quality of sugar beet. The optimal application rates of microbial fertilizer were 201.9-215.6 and 202.4-213.4 kg/hm² in flat cropping and ridge cropping. [ABSTRACT FROM AUTHOR]