A high-frequency signal double-layer flat cable adapter card that is capable of eliminating transmission disorder of a double-layer cable caused by paralleling and overlap of high-frequency signals and a direct current power supply loop. The high-frequency double-layer flat cable adapter card comprises a first connecting end, a second connecting end and a flat cable group formed by at least two strips of flat cables. The first connecting end includes a first substrate and a connector. The second connecting end includes a second substrate. The flat cable group is in an upper-lower dual-layer structure and is connected between the first connecting end and the second connecting end. A conductive metal foil sheet is arranged between upper and lower dual layers of flat cables of the flat cable group. The width of the metal foil sheet must cover areas of the flat cable group adopted as a power supply loop to isolate the magnetic field effect of the areas of the upper and lower dual layers of flat cables adopted the power supply loop.