A method for calibrating mismatches of an in-phase signal path and a quadrature signal path of a transmitter, including: utilizing the receiver to receive at least a test signal via the first signal path and the second signal path, wherein each test signal possesses a specific frequency within a specific frequency band; calculating at least a calibration coefficient for each test signal respectively, so as to calibrate mismatch between the first signal path and the second signal path of the receiver with respect to the specific frequency corresponding to each test signal; deriving a tap coefficient of a calibration filter of a calibration filter unit according to the at least a calibration coefficient of each test signal; and utilizing the calibration filter unit to calibrate a received signal.