Root C and root-released C are closely related to soil organic matter content and mechanistic simulation modeling has proven to be useful for studying root and soil organic C dynamics in plant-soil ecosystems.A computer model was designed in this study to simulate the dynamics of root C and root released C decomposition in situ and the dynamics of different forms of C in soil under two barley cultivars(Abee and Samson).The results showed that on the 15th day,about 48%of the total 14C fixed in roots was respired for Abee and 42%for Samson.This indicated that the turnover rate of root 14C of Abee was higher than that of Samson.The percentage of water-soluble organic 14C,active microbial 14C and stable 14C over the total fixed 14C were not different between two barley cultivars.From the analysis of the model for two barley cultivars,the total 14C transformed into different soil pools(excluding CO2-C and root C pools)for the two barley cultivars was similar(26%for Abee and 25%for Samson),but the difference of 14C remaining in soil between the two barley cultivars was mainly because of the difference of 14C remaining in roots which have not been yet decomposed.Some of the information which could not be measured in the laboratory conditions was obtained in this study. Root C and root-released C are closely related to soil organic matter content and mechanistic simulation modeling has proven to be useful for studying root and soil organic C dynamics in plant-soil ecosystems. A computer model was designed in this study to simulate the dynamics of root C and root released C decomposition in situ and the dynamics of different forms of C in soil under two barley cultivars (Abee and Samson). The results showed that on the 15th day, about 48% of the total 14C fixed in roots was respired for Abee and 42% for Samson. This indicates that the turnover rate of root 14C of Abee was higher than that of Samson. Percentage of water-soluble organic 14C, active microbial 14C and stable 14C over the total fixed 14C were not different between two barley cultivars. Flash the analysis of the model for two barley cultivars, the total 14C transformed into different soil pools (excluding CO2-C and root C pools) for the two barley cultivars were similar (26% for Abee and 25% for Samson), b ut the difference of 14C remaining in soil between the two barley cultivars was mainly because of the difference of 14C remaining in roots which have not been yet yet decomposed. Some of the information which could not be measured in the laboratory conditions was obtained in this study.