Abstract: Provided is an electro-optical phase modulation system, including: an electro-optical crystal, a radio frequency circuit and a light source, light incident surface of the electro-optical crystal is in parallel with light exit surface, upper electrode surface thereof is in parallel with lower electrode surface, and an angle between light incident surface and upper electrode surface is Brewster angle; two electrodes of radio frequency circuit are connected to upper and lower electrode surfaces respectively, for transmitting radio frequency signals to upper and lower electrode surfaces, so that an electric filed, direction of which is perpendicular to upper electrode surface, is formed between upper and lower electrode surfaces; light source is located at a side of light incident surface, and incidence angle of beams from light source with respect to light incident surface is Brewster angle. The system is used to reduce residual amplitude modulation, and increase accuracy of phase modulation.