Abstract: This paper describes the measuring principle and the method for outgassing and balance pressure of the liquid insulation medium（Edisol Ⅲ: PXE: IPB=1:1） at different temperatures and vacuum degrees,analyses and studies the property of the medium’s autgassing and its variation. Provides the theoretical data for the vacuum degassing purification and vacuum dry of liquid medium.The results of tests indicate that is is a kind of good insulation medium or impregnate full film power capacitor.