Nanofiltration membrane for extracting lithium from salt lake and preparation method of nanofiltration membrane

The invention discloses a nanofiltration membrane for extracting lithium from a salt lake and a preparation method. The preparation method comprises the following steps: step 1, preparing a polymer-based membrane; step 2, preparing a water phase solution; 3, preparing an organic phase solution; and step 4, interfacial polymerization reaction. The nanofiltration membrane prepared by the method comprises a non-woven fabric base layer, a hydrophilic porous support layer and a polyamide separation layer. Crown ether molecules are contained in the polyamide layer, and crown ether has the function of being specifically combined with lithium ions and can become an exclusive transmission channel of the lithium ions, so that the permeation efficiency of the lithium ions is improved, and the magnesium-lithium separation efficiency is improved. The preparation process is simple, the magnesium-lithium separation efficiency is high, and the method has a good application prospect in the aspect of salt lake lithium extracti