The termination resistor calibration circuit and a control method thereof are provided. The resistance of the termination resistor of the CML transmitter is directly calibrated, so that the error caused by duplicating the resistor can be avoided, which improves the calibration accuracy. In addition, no duplicated resistor and constant current source is required, which reduces the area occupied by the circuit. Further, the absolute current and the relative current are obtained from the bandgap module and thus have high accuracy. The output signal control module, the constant current source, and the termination resistors of the CML transmitter can be used for transmitting signals after the resistance calibration is finished, which improves the utilization of the circuit module.