Aiming at the requirement of high precision, fast and real-time polarization measurement, a polarization parameter measurement method based on double elastic optical difference frequency modulation is proposed. The principle of polarization measurement is analyzed in detail, and a multi-channel digital phase-locked data processing scheme based on Field-Programmable Gate Array (FPGA) is designed for the work control and signal demodulation requirements of the dual photoelastic modulator. The FPGA provides a Pulse Width Modulation (PWM) wave with a certain frequency duty cycle, and outputs a sinusoidal high voltage through the high voltage resonant circuit to drive the elastic optical modulator to work., at the same time, the modulated optical signal detected by the detector is converted by analog to digital, the Analog to Digital Converter (ADC) enters into the FPGA after acquisition. The FPGA provides a local reference signal to complete the simultaneous demodulation of multiple frequency signals, and then a single measurement the four parameters of the Stokes vector can be obtained. An experimental system was built for experimental verification, and a polarization generating device was established by rotating 1/4 wave plate method, which realized the measurement of linearly polarized light, circularly polarized light and elliptically polarized light. The experimental results show that the relative error of the system's measurement is less than 0.8%, the repeatability standard deviation is less than 0.2%, and the single measurement time is less than 200ms, realizing high-precision, repeatable, real-time polarization measurement.