To address the problem of AC/DC mixed field measurements, a rotary optical sensing element based on the electro-optical crystal Pockels effect is designed, which is not only suitable for measuring AC/DC mixed fields, but also suppresses fluctuations and errors in measurements. The principle of sensing when measuring DC electric field, AC electric field and mixed field by rotary optical electric field sensor is derived separately. In order to distinguish the electric field intensity at different frequencies, the Hilbert-Huang time-frequency conversion technique is applied to optical electric field measurements and the measurement scheme at different frequencies is given. After the calibration of the optical integrated sensor, the mixed field is measured. The experimental data show that the proposed optical electric field integrated measurement mechanism is suitable for the accurate measurement of AC and DC mixed fields.