The invention provides a method for preparing a multilayer microporous membrane for lithium ion batteries. Polyolefin resin and auxiliary additives are used as raw materials to obtain a melt after melting and plasticizing, extruding through a die head, and tape-casting to obtain an intermediate Membrane: Take multiple rolls of the intermediate film, compound it through a composite device with transverse stretching function, obtain a composite intermediate, anneal it under bidirectional micro tension, and stretch it longitudinally to obtain a multilayer microporous membrane for lithium ion batteries . In the present invention, the compounding roll is heated during the compounding process of the intermediate film, and the crystallization of the polymer structure inside the intermediate film is further improved. At the same time, the transverse extension is carried out under slight tension, and the degree of transverse orientation is increased, so that the prepared microporous film has uniform micropores. , the lateral strength is improved, the ability to resist lithium dendrite piercing is effectively improved, and micro-short circuits are avoided, which is suitable for large-scale production. The multilayer microporous membrane prepared by the invention has high structural uniformity, and has obvious effect on improving the safety performance of the battery.