Based on the principle of the Pockels effect, the electro-optical sensing unit and the electric field modulation mechanism in the AC-DC hybrid strong electric field sensor are designed and tested. Reasonably design the structure of the electro-optical sensor unit, select and prepare related devices. The test platform was built, and the test results showed that the input and output of the electro-optical sensor unit had good linearity, had a fast response to the change of the electric field waveform, and had good frequency characteristics. Its performance met the needs of measuring the modulated electric field waveform. The electro-optical sensing unit and the electric field modulation mechanism are used to construct a sensor to measure the strong AC and DC electric field.