A second-generation high temperature superconducting (HTS) strip and a preparation method thereof are provided. The second-generation HTS strip includes a superconducting strip body and a stabilizing layer arranged thereon. The stabilizing layer is a copper-graphene composite film with a total thickness of 2-30 microns on one side. The superconducting strip may be obtained by the preparation method of: (1) putting a superconducting strip body into a magnetron sputtering reaction chamber, followed by pumping to a high-level vacuum and filling with a working gas; (2) using copper and graphene as targets, and performing a sputter coating by controlling a magnetron sputtering power, to deposit the targets onto at least one surface of the superconducting strip body. The prepared HTS strips containing copper-graphene stabilizing layer with high strength and high conductivity may have 30%-70% higher tensile strength than conventional copper plated superconducting strips, with less than 10% IACS attenuation in conductivity.