A hard drive tray device applied in a server is provided. The server includes a housing. The hard drive tray device includes a rail member and a tray. The rail member is disposed at the inner wall of the housing. The tray is slidably engaged with the rail member so as to slide between an expanded position and a closed position relative to the housing. The tray includes a base for carrying two storage devices. The base has a hollow portion. The storage devices are respectively located at two sides of the hollow portion. When the tray slides to the expanded position, one of the storage devices and at least a part of the hollow portion are located outside the housing.