An antenna assembly and an electronic device are provided according to the present disclosure. The antenna assembly includes an antenna module and a bandwidth matching layer. The antenna module is configured to transmit and receive, within a preset direction range, a millimeter wave signal in a target frequency band. The bandwidth matching layer is spaced apart from the antenna module, and at least part of the bandwidth matching layer is disposed within the preset direction range. The bandwidth matching layer is configured to match an impedance of the antenna module to an impedance of free space to enable an impedance bandwidth of the antenna module in the target frequency band when the bandwidth matching layer is provided to be greater than an impedance bandwidth of the antenna module in the free space.