An electronic device with time update function includes a radio module, a clock module, an audio input port, a storage module, and a processing module. The radio module receives and outputs audible signals from the broadcasts of a broadcasting station. The audio input port receives audible sound generated by the radio module, and the clock module provides a source of real time. The processing module determines whether the signals received by the audio input port include current time information, and if so whether the system time is consistent with the current time information. The processing module updates the stored initial time with the current time information and adjusts the system time as necessary. A time update method is also provided.