The invention relates to the field of a lithium-ion battery and specifically discloses a lithium-ion battery diaphragm, a polyethylene compound for the lithium-ion battery diaphragm, a preparation method thereof and the lithium-ion battery. The polyethylene compound includes polyethylene, a pore-forming agent, a cross-linking agent and cross-linking auxiliaries, wherein the melt index MI of polyethylene is 0.02g/10min-6g/10min; and when the content of polyethylene is 100 weight parts, the content of the cross-linking agent is 0.03-8 weight parts, the content of cross-linking auxiliaries is 0.03-10 weight parts and the content of pore-forming agent is 54-160 weight parts. The polyethylene compound can be adopted for preparing the lithium-ion battery diaphragm with high heat resistance.