A self-locking fixing device and an antenna assembly are provided. The self-locking fixing device includes an inner mandrel arranged to include a nail head and a nail rod extending away from the nail head, and a bushing arranged to include a nail head bushing and a nail rod bushing extending away from the nail head bushing. A sidewall of the nail head bushing is provided with at least two elastic clamping units. If the inner mandrel is assembled with the bushing, the nail head is located in the nail head bushing, the nail rod is located in the nail rod bushing, and clamping portions of the elastic clamping units are engaged with an upper surface of the nail head to clamp the nail head in the nail head bushing.