A DC offset calibration apparatus including a signal processing unit, a comparison unit, a first resistor array, a second resistor array, and a resistor array control unit is provided. The signal processing unit receives an input differential signal and generates an output differential signal. The comparison unit detects and determines a first DC output voltage and a second DC output voltage of the output differential signal and generates a DC offset signal. First ends of the first resistor array and the second resistor array are respectively coupled to a first input terminal and a second input terminal of the signal processing unit. The resistor array control unit adjusts resistances of the first and the second resistor array according to the DC offset signal and a bit code sequence until the DC offset signal enters a transient state, so as to calibrate a DC offset voltage in the output differential signal.