Based on a 18-year-long experiment conducting at Baiyun experiment station in Wuwei City,theeffects of long-term fertilization on soil organic,inorganic and microbial biomass carbon in 0-20cm layer ofirrigated desert soil were analyzed.The results showed that long-term combined application of nitrogen andorganic fertilizer,as well as manure application led to increases of soil organic and microbial biomass carboncontents,while reduced soil inorganic carbon contents.Applying straw alone increased soil organic carbon,but had no significant impacts on inorganic and microbial biomass carbon levels.Long-term application of nitrogen fertilizer had no significant influence on soil organic,inorganic and microbial biomass carbon contents.All results revealed that soil organic carbon contents negatively correlated with inorganic carbon contents,and positively with soil microbial biomass carbon contents.