A long-term field experiment of a triple cereal cropping system(barley-double rice)has been carried on for 26 yrs.Results showed that continuous application of FYM increased SOM successively and eventually reached such a high level as 60g kg^-1 in SOM content while maintaining high crop yield.The quantity of FYM applied was one of the most important factors which affected the rate of SOM accumulation.A model for the change in SOM was developed.Only 4.8 tons FYM was needed to keep SOM in balance in the barley-double rice cropping system.