Electron Cloud Instability has been studied in the operation of BEPC.The BEPC Ⅱ began the commissioning in November 2006 and the positron beam current has reached 500 mA.Because of such a high beam current,some instabilities such as ECI,bunch lengthening et al,have appeared during the operation.The experimental investigation on ECI during the commissioning of BEPC Ⅱ will be reported in this paper.