In this letter,the liquid film is used for optical probing of electric field,whose voltage sensitivity is 2 orders of magnitude higher than the GaAs in the same system.The electro-optic coefficient is measured to be 95 pm/V at 1 kHz based on the mechanism of orientation polarization.It is a simple and high-efficiency method to probe integrated circuits with the liquid film,which facilitates measuring the voltage and waveform of weak signal under low frequency.