Change of soil organic carbon under no-tillage paddy—upland rotation was studied through filed investigation and laboratory analysis.Results showed that with the increasing years of no-tillage

the maximum soil organic carbon occurred 5 to 6 years after water-cultivation and dry-cultivation.The content of soil organic carbon under no-tillage was significantly different from that under conventional tillage.The content of soil organic carbon within 5 cm of the surface soil was obviously higher than that in other soil layers

suggesting a certain surface accumulation phenomenon.The ontent of fulvic acid was found to be higher than the content of humic acid after water-cultivation and dry-cultivation.Ratios of soil carbon to nitrogen were from 10 to 16

which is favorable to nutrient release during organic matter decomposition.Change in organic carbon density was the same as that in soil organic carbon.The study may clarify the effect of no-tillage practices on the content of soil organic carbon and provide a theoretical basis for building a reasonable crop rotation model and a scientific guidance for promoting the use of farming methods.