Soil salinization can limit the development of agriculture in the Yellow River Delta.In this paper,saline and alkaline farmland in the Yellow River Delta was chosen as the research object,and effects of soil salinity on soil microbial biomass nitrogen(SMBN) under different conditions were investigated to study the response of soil nitrogen turnover to salt stress.There were four salinity gradients(S1:0.1%;S2:0.5%;S3:0.9%;S4:1.3%),and four substrates were added to the soil.The results showed that after the addition of various substrates,SMBN in treatments with high soil salinity(S3 and S4) was obviously lower than that in treatments with low soil salinity(S1 and S2).In comparison with treatment S1,the average of SMBN in treatments S3 and S4 decreased by 35.8% and 46.7% respectively when there was no substrate added to them;it declined by 55.6% and 56.1% respectively as the carbon source was added to them;it reduced by 24.6% and 28.3% when the nitrogen source was added to them;it dropped by 43.8% and 57.0% respectively as the carbon and nitrogen source were added to them.Compared with treatments without substrates,the addition of the nitrogen source could not improve SMBN;the addition of the carbon source or carbon and nitrogen source could enhance SMBN obviously,and it increased by 60.9% and 66.1%(or 110.8% and 140.2%) in treatments with low soil salinity(S1 and S2),while it changed slightly in treatments with high soil salinity(S3 and S4).In order to increase SMBN,it is needed to apply organic fertilizer or chemical fertilizer and organic fertilizer to maintain or improve soil fertility. Soil salinization can limit the development of agriculture in the Yellow River Delta. In this paper, saline and alkaline farmland in the Yellow River Delta was chosen as the research object, and effects of soil salinity on soil microbial biomass nitrogen (SMBN) under different conditions were investigated to study the response of soil nitrogen turnover to salt stress. There were four salinity gradients (S1: 0.1%; S2: 0.5%; S3: 0.9%; S4: 1.3% The results showed that after the addition of various substrates, SMBN in treatments with high soil salinity (S3 and S4) was obviously lower than that in treatments with low soil salinity (S1 and S2). In comparison with treatment S1, the average of SMBN in treatments S3 and S4 decreased by 35.8% and 46.7% respectively when there was no substrate added to them; it declined by 55.6% and 56.1% respectively as the carbon source was added to them; it reduced by 24.6% and 28.3% when the the nitrogen source was added to them; it dropped by 43.8% and 57.0% respectively as the carbon and nitrogen source were added to them. Compared with treatments without substrates, the addition of the nitrogen source could not improve SMBN; the addition of the carbon source or carbon and nitrogen could could enhance SMBN obviously , and it increased by 60.9% and 66.1% (or 110.8% and 140.2%) in treatments with low soil salinity (S1 and S2), while it changed slightly in treatments with high soil salinity (S3 and S4). In order to increase SMBN, it is needed to apply organic fertilizer or chemical fertilizer and organic fertilizer to maintain or improve soil fertility.