This paper reviews and analyzes IT Capability of electronic commerce enterprises in the different stages and on the basis of "stimulusresponse" model using case analysis method. The study found that in IT supports business stage, the responding mechanisms of EC enterprise to cope with external changes are mainly the guarantee mechanism and part of the emergency mechanism, and outputting IT infrastructure capability; in IT and business integrating stage, the response mechanisms enriching gradually, including early warning mechanism, coordination mechanism and emergency mechanism, outputting IT business spanning capability; and in the IT leading business stage, planning system becomes increasingly important among the response mechanisms, outputting IT proactive capability.