The embodiment of the invention provides a protecting method, a device and a system of a memory device. The protecting method of the memory device comprises the following steps: sending an authentication message to a server, so that the server can authenticate the memory device according to the authentication message; and when the authentication passes, charging and magnetizing an electronic magnet in the memory device, so that the memory device can be opened by the electronic magnet. In the embodiment of the invention, data security in the memory device is improved.