In order to solve the problem of water pollution caused by the accumulation of ammonia nitrogen, the fungus can degrade ammonia nitrogen efficiently and tolerate salt was isolated from the saline land of Shanyin County, Shuozhou, Shanxi Province, China. The fungus was identified as Fusarium sp. and named X-8 by morphological observation and ITS sequence homology analysis, and further analysed the effects of single and multi factors on the degradation of ammonia nitrogen under different environmental conditions (temperature, pH, inoculum amount, initial ammonia nitrogen concentration, salt concentration, C/N), and carried out three-factor, three-level orthogonal tests. The results showed that the degradation rate of ammonia nitrogen by X-8 could reach 93.47% when the temperature was 37.37℃, pH was 8.12, and the inoculum amount was 4.72 g/L.