The invention discloses a lithium battery diaphragm preparation method based on a mixed solvent multi-stage volatilization mechanism. The preparation method comprises the steps of performing heating dissolution on a certain mass of PVDF-HFP in a certain mass of first solvent, performing normal temperature dissolution on a certain mass of PVDF-HFP in a certain mass of first solvent, enabling the above two parts to be mixed uniformly and then adding a certain mass of second solvent, performing uniform mixing and than coating a base material, and carrying out drying to obtain the lithium batterydiaphragm. According to the preparation method, the PVDF-HFP is added into the first solvent in two times to form a cross-linked network structure with link; then the second solvent is added to dissolve a part of the link, and the dissolved partial link forms the cross-linked network structure to wind around the linkage; after drying, the first solvent is volatilized to form main lithium ion transmission holes; and the second solvent is volatilized to form holes in the cross-linked network structure around the link, so that the surrounding strength of the link of the lithium battery thin filmis reinforced, and the strength of the lithium battery diaphragm is further reinforced.