A measuring device for a hard disk drive includes a first input node, a hard disk drive having a first input terminal, the first input terminal being coupled to the first input node to provide power to the hard disk drive. A first input current sampling unit is coupled between the first input node and the first input terminal of the hard disk drive to obtain a first input current Iin1. A first input voltage sampling unit is coupled to the first input terminal of the hard disk drive to obtain a first input voltage Uin1. A control unit is coupled to the first input current sampling unit and the first input voltage sampling unit to receive the first input current and the first input voltage.