Abstract: A class 1E cable for a third generation passive nuclear power plant in a mild environment, comprising: at least one conductor; wherein an heterogeneous double-layer co-extrusion insulator is extruded on an external wall of the conductor, a wrapping tape is wrapped around the heterogeneous double-layer co-extrusion insulator to form a wire core, and the wire core is provided in a filler; a shielding layer 6, an oxygen barrier layer an inner protection jacket layer, and an outer protection jacket layer are wrapped around the filler; the heterogeneous double-layer co-extrusion insulator comprises an inner insulating layer and an outer insulating layer, wherein the inner insulating layer and the outer insulating layer are made of different materials; and the inner protection jacket layer and the outer protection jacket layer are made of different materials.