Through use of the principal component analysis (PCA) and cluster analysis (CA) methods,sensitivity was analyzed of characteristic indices of changes in organic carbon in soils subject to straw application and earthworm (Metaphire guillelmi) activity in a long-term rice- wheat rotation field experiment,Results show that these indices varied in response to straw application and earthworm activity.When all the indices chosen were used,the changes in content and composition of soil organic carbon could be reflected relatively inextenso,but too much information and inconsistency of the information embarrassed further analysis.According to the principal component analysis (PCA) and cluster analysis (CA) methods,these indices could be divided into two groups,one related to soil organic carbon content,including dissolved organic carbon (DOC),hot water extractable carbon (HWEC),potentially mineralizable carbon (PMC),basal respiration (BR),acid extractable carbon (AEC),readily oxidation carbon (ROC),particulate organic carbon (POC),light fraction organic carbon (LFOC),total organic carbon (TOC),and the other related to microbes and having some potential influence on soil organic carbon,including microbial quotient (Mq),qCO₂ and microbial biomass carbon (MBC),The former could be used to evaluate effect of straw application on soil organic carbon,and the latter to evaluate potential effect of earthworm activity on soil organic carbon.