A data protection method for protecting backup data stored in a data backup device is executed by a mobile device. When the mobile device is included in a trust circle of the data backup device, the mobile device can receive a certified signal, can execute a file manager of a backup APP for loading the backup data, and can generate a first invitation code. Otherwise, the mobile device cannot access the backup data, and displays a code input menu for inputting a second invitation code. The data backup device can certify the first invitation code and the second invitation code for determining whether the mobile device can be added into the trust circle of the data backup device. Therefore, the mobile device included in the trust circle can access the backup data, and the privacy of the backup data can be secured.