The invention relates to a signal demodulation system, which includes a polarizer, an optical rotator, an optical crystal, a polarizer, a photodetector, a preamplifier, a low-pass filter, and a control module. The optical crystal, the polarizer and the photodetector are connected in sequence, and the preamplifier and the low-pass filter are connected to the output end of the photodetector. The signal demodulation system of the present invention can meet the high stability optical rotation data processing requirements, and the system has simple operation, intuitive interface, short development cycle, low cost, industrial production and use, and strong practicability.