For researching the effect of optimized fertilizer on soil chemical properties of switchgrass fields and the influence on the bacterial diversity structure and diversity，different types of surface soil planted with three-year switchgrass in saline wasteland and switchgrass fields in half arid areas were studied using high-throughput sequencing technologies，different nitrogen application rates(0，60，120 and 240 kg·hm-2)were adopted and the saline wasteland was used as CK.The results showed that，in general，nitrogen application significantly reduced soil pH and total salt content，and increased soil nutrient content and soil chemical property.Compared with saline wasteland(CK)，soil pH and total salt content decreased by 3.32%～11.53% and 43.27%～73.32%，respectively，and soil nutrient content increased by 14.05%～20.98% in switchgrass fields.74000 valid sequences were obtained from the five treatments with 15 soil samples，based on the similarity level of 97% or more，through clustering analysis of operational classification unit(OTU)categorization，CK，N0，N60，N120 and N240 had an average of 8696，9210，9403，8450 and 8239 OTU types，respectively，Chao1 index，ACE index，and Shannon index were 6623.06～7627.90，7457.14～8412.28 and 6.40～6.67，respectively.Among the soil samples of five treatments，bacterial populations were relatively consistent at the classification level of phylum and genus，and dominant phylums were mainly Proteobacteria，Actinobacteria，Acidobacteria，Bacteroidetes and Bactertomyoetes，with relative abundance accounting for 75.74%～91.30%.The dominant genera were Sphingomonas，Gp6，Gemmatimonas，Ohtaekwangia，Arthrobacter，Subdivision3 Genera Incertae Sedis，Pseudomonas，Sphingobium，Geminicoccus and Aridibacter，with relative abundance of 55.72%～62.98%.The hierarchy clustering and correlation analysis showed that the application of nitrogen fertilizer had a certain effect on the bacterial diversity structure，in which the total salt，available phosphorus，available potassium，organic matter，total nitrogen，total phosphorus and alkali-hydrolyzed nitrogen content were the main physical and chemical factors that affect the bacterial communities of Pseudomonas and Aridibacter.In conclusion，fertilization significantly increased soil nutrient content and changed soil physical and chemical properties，but did not change soil bacterial diversity in switchgrass field.