The in-situ calibration technology of phased array radar antenna has been researched. The principle of phased array antenna in-situ calibration based on the microwave photonic technology was introduced. By taking advantage of Pockels effect of the electro-optical crystal in the optical probes erected on the phased array antenna, the optical signal reflected from the probe was modulated by the measured electromagnetic field. Then the amplitude and phase information of the measured phased array antenna units can be obtained through photoelectric conversion and coherent detection of the optical signal. Experimental results demonstrate that the measurement amplitude and phase accuracy of radiation electromagnetic field respectively reach 0.3 dB and 2°. And this calibration method has the advantages of low aggressiveness, strong anti-jamming ability, small volume, etc. which can meet the practical demands of phased array antenna calibration and have very strong engineering practical value.