Biological soil crusts (BSCs) play an essential role in the geochemical cycling of nitrogen in drylands. To explore the variation in the content of different nitrogen forms under different BSCs and their affecting processes and extents can help further understand the ecological functions of BSCs. This study was carried out on two types of BSCs, namely algal-lichen mixed crusts and moss crusts (with bare sand as the control), in the Gurbantunggut Desert. The soil samples were obtained from BSCs and eight depths within 0 to 100 cm under BSCs. The contents of nitrogen pools such as total nitrogen, inorganic nitrogen, soluble organic nitrogen, free amino acid nitrogen and microbial biomass nitrogen, and the activities of extracellular soil enzymes such as soil urease, nitrate reductase and leucine aminopeptidase were measured. The results showed that:1) the content of each nitrogen form and soil enzyme activities in the BSCs were significantly higher than those in the soil beneath them. Overall soil nitrogen pool in the BSCs and the different depths beneath them were moss crusts > mixed algal-lichen crusts > bare sand. Vertical distribution of each nitrogen form and soil enzyme activity showed a trend of first decreasing significantly (0-20 cm) and then stabilization (20-100 cm) from surfaces of BSCs to 100 cm depth. In the 20-30 cm soil depth, the content of available nitrogen (inorganic, nitrate and ammonium nitrogen) was characteristically increased, except for inorganic and ammonium nitrogen in bare sand and nitrate nitrogen in the mixed algal-lichen crusts. 2) The content of each soil nitrogen form was positively correlated with soil total phosphorus, organic carbon, electrical conductivity, soil urease and leucine aminopeptidase activities, and was negatively correlated with pH and soil water content. 3) The multifunctionality index of soil N cycle was established using N cycle-related indices, and the index in the 0-100 cm soil depths showed similar pattern with the distribution of soil nitrogen pool. Therefore, with the development of the BSCs, the nitrogen pool accumulated. The influence of BSCs on the soil nitrogen pool was mainly concentrated in the 0-20 cm depths, with less influence on the nitrogen pool in the deeper layers of the soil. Some other nutrient elements were also changed with the variations in nitrogen pools.