Based on the wetland in the Sanjiang Ecology Station of Chinese Academy of Sciences,the characteristics of soil enzyme activity and fertility under different types of land use,including wetland ecosystem,dryland ecosystem,conversion from dryland to wetland,conversion from dryland to forestland,were investigated.The results showed that there was great significance between the soil enzyme activity(invertase,urease,phosphatase,and catalase),the contents of organic carbon and soil nutrients under different types of land use,they were the highest in the unreclaimed wetland,20 years after the wetland was reclaimed,the enzyme activity,the contents of organic carbon and soil nutrients all declined greatly than that in wetland,when the reclaimed dryland was recovered to wetland,the enzyme activity,the contents of organic carbon and soil nutrients increased significantly than that in dryland,however,when the reclaimed dryland was recovered to forestland,the contents of all above components were also increased at a different extent than that in dryland.Therefore,it is imperative under the situation to recover the wetland from dryland so as to keep high soil fertility and biological activity,and to maintain the stability of organic carbon in the wetland of Sanjiang plain.