This paper first introduces the concepts( SCR, ESCR, QESCR ,H, and VSF.) and their usage. Later MIIF, equivalent admittance, MISCR and MIESCR, PBR are detailedly expounded. This paper put forward to the steps of the primary steady voltage stability work , detailed scheme of the steady voltage stability, the studing methods of the transient voltage stability in the multi-infeed AC/DC system. At last, the online voltage stability and the virtual smart power grid were put forward.