A separator including a porous substrate layer, an intermediate layer, and a ceramic coating layer is provided. The ceramic coating layer is disposed on a side of the intermediate layer away from the porous substrate layer. The intermediate layer includes a metal oxide powder. The particle diameter of the metal oxide powder is less than the pore diameter of the porous substrate layer, and at least a portion of the metal oxide powder is embedded in the porous substrate layer. A method of preparing the separator and a lithium-ion battery including the separator are also provided.