Disclosed in the present invention is an isolating membrane of an electrochemical device, comprising a modified porous base membrane and a functional layer arranged on the surface of at least one side of the modified porous base membrane. The functional layer contains slurry of organic matter and inorganic matter compounds, and the modified porous base membrane contains particles of a lithium-containing conductive ion compound. According to the present invention, the lithium-containing conductive ion compound is prepared by adopting a sol-gel-hydrothermal method, and small-particle-size particles of the lithium-containing conductive ion compound are embedded into the isolating membrane base membrane, so that the defects of poor ionic conductivity and poor wettability of an existing isolating membrane are overcome, and moreover, the isolating membrane has good adhesion and heat resistance due to the coated functional layer.