Optical electric field probes have been gradually applied to measure the radiation capability of phased array radar antennas. Therefore, more attention is paid on how to accurately measure the amplitude and phase of this method. This paper introduces the idea of electric field probe calibration, and proposes a method of using electric field of the rectangular metal waveguide to generate a standard signal containing amplitude and phase to calibrate the optical electric field probe’s measurement capability. The design and production of the calibration device is elaborated in this paper. Experiment results show that this method is able to calibrate the optical electric field probe’s measurement capability, and the precision meets the requirements.