An electronic device includes an input unit, a processing unit and a coding/decoding system. The coding/decoding system includes a reflector array, a knob group, an infrared emission unit, an infrared receiving unit and a coding/decoding unit. The reflector array includes at least one mirror mounted rotatably in the electronic device. The knob group is configured for adjusting angles of the reflector array. The infrared receiving unit is configured for receiving infrared rays reflected by the reflector array and generating a password signal according to the received infrared rays. The coding/decoding unit is configured for receiving the password signal and converting the password signal into a password. The coding/decoding unit stores the password and locks the electronic device according to the password. To unlock the electronic device, the coding/decoding unit compares the password with a pre-stored password to determine whether to unlock the electronic device.