The invention relates to a battery tray, a battery tray assembly and an electric vehicle. The battery tray comprises a tray bottom plate and an installation beam, wherein the tray bottom plate is used for fixing and supporting a battery, the installation beam is arranged around the tray bottom plate, and the battery tray is characterized in that a cavity is formed in at least one edge of the installation beam. By arranging a cavity structure in the installation beam, the material dosage is greatly reduced, and the cost is reduced; and meanwhile, the whole power battery is more convenient to install, the installation process is simplified, the installation efficiency is improved, and the strength of the whole battery installation structure is also ensured.