In this paper,a measurement method based on small signal is proposed to solve the problems of complex high frequency half wave voltage measurement method and expensive instrument of M Z electro optic intensity modulator.By using the integral characteristics of the optical power meter and using only the light source,signal generator,DC power supply and optical power meter,the high precision measurement of high frequency half wave voltage of M Z electro optic intensity modulator can be achieved by measuring the change of the extreme output power of the device with and without RF signal input.In addition,the simulation verification of the measurement method is carried out by using OptiSystem,measurement error analysis is performed with Matlab,and the measurement method is verified at 1 kHz frequency.Simulation and experimental results show that the proposed method can accurately measure the half wave voltage of M Z electro optic modulator only with small signal.The absolute error at 1 kHz is less than 0.5%,and the relative error is less than ±0.3 dB in the range of 10 MHz～40GHz.