The invention provides a mobile electronic apparatus capable of assisting a car radio in tuning a radio channel. The mobile electronic apparatus of the invention accesses current location information by a GPS module thereof, then according to the current location information and a look-up table, determines a channel, and finally, transmits a signal representative of the determined channel to the car radio. The car radio converts the signal into the determined channel information and tunes the radio channel to the determined channel. Therefore, a user just needs to input a requested radio station, so as to make the car radio tune the radio channel by the mobile electronic apparatus automatically.