The invention discloses a lithium battery separator. The lithium battery separator comprises the following constituents based on percent by mass: 90-99.9% of film formation polymer and 0.1-10% of natural organic additive containing a sulfur compound and/or a mercaptan compound and/or a sulfonic compound, wherein the film formation polymer is polyvinylidene fluoride-hexafluoropropylene and/or polyvinylidene fluoride, and the natural organic matter additive is dried natural organic matter powder. The invention discloses a preparation method of the lithium battery separator. The natural organic additive containing the sulfur compound and/or the mercaptan compound and/or the sulfonic compound is added to the film formation polymer, the film formation polymer of a cross-linking net-shaped structure, molecular chain of the film formation polymer is inserted into holes of the natural organic matter powder, and the natural organic matter powder forms chains in the cross-linking net-shaped structure. By the lithium battery separator, the strength of the lithium battery separator is effectively improved, and lithium dendrites is prevented from being easily punctured through the lithium battery separator.