The invention discloses a diaphragm for a lithium ion battery. The diaphragm is composed of a base membrane and coatings covering two sides of the base membrane, wherein each of the coatings is prepared from the following components: alkylolamide polyoxy ethane ether, calcium dihydrogenphosphate, nano silicon-aluminum powder, tannic acid, sodium polyacrylate, sec-alkyl sodium sulfonate, butyl acrylate, butyl acrylate, succinate and ceramic powder. The diaphragm for the lithium ion battery disclosed by the invention has the advantages of being high in strength and high in oxidization resistanceand heat stability.