1. A powerless smart key comprising: a receiver coil; a current receiver electrically coupled to the receiver coil, and configured to receive electric energy via the receiver coil such that the powerless smart key is powered directly by the received electric energy and then the powerless smart key works; a fingerprint capturing unit coupled to a storage unit and configured to obtain a fingerprint image of a user and further store the fingerprint image in the storage unit; a controller configured coupled to a wireless transmit unit with the storage unit and configured to control the wireless transmit unit to transmit a wireless signal containing the fingerprint image to an intelligent entrance guard unlocking system; a current convertor electrically coupling the current receiver with the controller; and a current-stabilizing unit electrically couple the current receiver with the current convertor and configured to stabilize current of the received electric energy to prevent the current to exceed a predefined value suddenly; wherein, another controller of the intelligent entrance guard unlocking system is configured for receiving the wireless signal, and determining whether the powerless smart key is matched with the intelligent entrance guard unlocking system according to the fingerprint image.