Abstract: In order to understand the effects of nitrogen fertilizer on biomass amount and soil enzymes activity of desert grassland，field experiments about nitrogen(N) fertilization on three different precipitation desert grasslands were carried out in Shihezi, Xinjiang ,China. Grass biomass amount and soil enzyme activity of urease, proteasse, invertase, alkaline phosphatase, polyphenol oxidase and catalase were explored. Results showed that grass biomass amount and soil enzyme activities of treatments with the application of N fertilizer increased. The grass biomass amount increased by 21.8%-78%,21.7%-39.3% and 26.3%-31.4% in higher, middle and lower precipitation areas , respectively. Soil enzyme activities of urease, proteasse, invertase and alkaline phosphatase with the application of N treatments increased at the beginning then decreased with days after the fertilizer applied, but polyphenol oxidase and catalase activities increased. Polyphenol oxidase activities increased at the beginning and then decreased with soil depth increasing，while other 5 enzyme activities decreased. Soil enzyme activities of urease, proteasse, invertase and alkaline phosphatase decreased with the decrease of precipitation, but polyphenol oxidase and catalase activities were maximum in middle precipitation area.