The structure characteristics of the independent local power grid are summarized firstly.Then,the security and stability problem of the local power grid is analyzed,combined with the development trend of the state promoting sales side reform.Three lines of defense construction scheme are proposed taking an independent local power grid as an example.Some key technical problems related to the stability control system,low frequency and low voltage load shedding,high frequency cutting machine,out-of-step splitting solution are discussed.The applicability of the scheme is verified by RTDS and off-line simulation,the feasibility of on-line and real-time stability control system is demonstrated.Finally,the construction principles of the three lines of defense for the independent local power grid are summarized.