The array of a large active phased array antenna has hundreds of thousands or even tens of thousands of transceiver modules and radiation units. It makes the phased array antenna more complex than other types of antennas and thus difficult to maintain. The present situation of array calibration is introduced firstly in the paper, and then the calibration test is carried out by using the method of external calibration. This method realizes automatic calibration of the antenna array and improves the efficiency and precision of the array calibration. The test results show that the coupling amount within the frequency band between the radiation units is stable between -30 dB and -70 dB. The design index is consistent with the test results.