The invention discloses a thermal self-closing ceramic modified diaphragm and a preparation method thereof, and belongs to the technical field of lithium battery diaphragms, the thermal self-closing ceramic modified diaphragm comprises a polyolefin diaphragm substrate, at least one surface of the polyolefin diaphragm substrate forms a corona treatment surface, and the corona treatment surface is coated with a thermal self-closing ceramic coating. The invention discloses a preparation method of a thermal self-closing ceramic modified diaphragm. The method comprises the following steps: S1, preparing a thermal self-closing ceramic coating, S2, unwinding the polyolefin diaphragm base material; S3, carrying out corona treatment on the coated surface of the polyolefin diaphragm base material; after corona treatment is finished, coating the thermal self-closing ceramic coating prepared in the step S1; and S4, drying and shaping the coated polyolefin diaphragm base material; and S5, after drying is completed, conducting rolling, conducting standing and curing for 6-8 days at the normal temperature, and obtaining the thermal self-closing ceramic modified diaphragm. The thermal self-closingceramic modified diaphragm and the preparation method thereof have the advantages that the thermal self-closing performance is achieved, the safety is improved, the thermal curing performance is achieved, and the diaphragm breaking temperature is increased.