A technique for demodulating the fiber Fabry-Pérot (F-P) cavity sensor is presented based on the dual-path and dual-wavelength demodulation principle. The dual-path sensor system is constructed. Theoretical analysis, simulation calculations and experimental result of the dual-path and dual-wavelength demodulation F-P cavity sensor are presented. It is proved that the method can eliminate errors resulting from wavelength-independent variations in the fiber interconnected to the sensor. According to the known initial cavity length and reflectivity, two operating wavelengths and their bandwidths are determined by optimal parameter selection. After least square fitting, the related linear regression coefficient of the experimental result is 98.35%. The experimental results show that the method can satisfy the demands of sensitivity, response speed and stability at the same time.