The on-site calibration of antennas is getting much more attention now because it can greatly impact the performance of the phased array radar. This paper introduces the current situation of on-site calibration of antennas and puts forward some existent problems. It focuses on analysing the advantages of optical-electromagnetic field detect technique and proving on-site calibration of phased array radar antennas based on optical technology is entirely feasible, by building the on-site calibration device and doing some experiments. This technology can calibrate parameters of phased array radar antennas accurately and have less impact on radiation field of antennas. It can meet the requirements of the on-site calibration of phased array radar antennas.