Provided is an RFID system and method for maintaining a constant strength of a signal transmitted from an RFID tag to an RFID reader, regardless of a distance between the reader and tag. The RFID signal strength measuring reader measures a signal strength received from the RFID tag, creates control information used to set an amplification amount of the RFID tag by using a value of the measured strength to include the control information in an output signal, and sends the output signal to the RFID tag. The RFID tag, if the signal sent from the RFID reader is received, extracts internal information from the received signal, sends the information to the RFID reader as an output signal, and extracts the control information included in the signal sent from the RFID reader to adjust a strength of the output signal according to a value of the control information.