Considering the shortcomings of large volume and high power consumption of the current multi-channel fiber Fabry -Perot pressure sensor demodulation system, this paper proposes a method to realize four channel demodulation through rapid and continuous switching of MEMS optical switch, selects a low-power CMOS image sensor s11639, and constructs a hardware demodulation circuit with FPGA as the core, The multi-channel switching logic constraints and the acquisition of interference spectrum are completed by writing s11639 and ad9826 drivers. Finally, the cavity length of the sensor connected to each channel is displayed in real time in the host computer through data processing and transmission. The calibration coefficient is determined by the standard demodulation instrument, and the cavity length of the four pressure sensors connected to the access is actually measured. There is no jumping point in the process of cavity length measurement, which shows that the four channel demodulation system designed in this paper has good calibration stability and small error. The nonlinearity of each channel is calculated according to the measured data. The maximum nonlinearity of the four channels is 0.93%, and the demodulation speed of each channel can also reach 10Hz.