In an incubation experiment, dynamic change in amounts of soil organic matter (SOM), HA and FA were studied during corn stalk (CS) decomposition in dark-brown soil by δ¹³C method.The results showed that organic carbon from both new added CS and original soil decreased, but decomposition rate of the latter was slower than that of the former during incubation periods.The residual rate of CS was about 36% at 360th day and 24% at 720th day, whereas that of original SOM was above 90% at 360th day and about 76% at 720th day.In the initial stage of incubation (1hour), the formed rate of FA was faster than that of HA.Then, FA transformed into HA.After 15th day, HA transformed into FA again.HA and FA from original SOM also transformed each other, and it was still the same trend that FA transformed into HA before 15th day.But the transformed rate in original SOM was relatively slower than that in new-formed SOM.δ¹³C method can be used to study decomposition dynamics of SOM in short-term incubation experiment (several months~several years).