In view of the complicated structure and high cost of the ever reported fiber-optic Fabry-Perot (F-P) sensing demodulator, a new demodulation scheme based on optical correlation is presented in this paper. A glass wafer is used as an optical cross-correlator. The cavity length of the F-P sensor is demodulated by the cross-correlation relationship between the glass wafer and the F-P cavity. To optimize the optical path, the single-mode fiber-optic F-P sensing demodulator with a simple structure has been constructed by establishing a simulation model. The demodulator consists of a broadband light source with the center wavelength of 850 nm, a glass wafer, a linear CCD, a cylindrical mirror and a single-mode fiber. Experimental results show that the resolution of the demodulated cavity length is achieved to be 0.72 nm. The proposed demodulator has broad prospects in the fields of well logging, liquid level monitoring and structural health monitoring for temperature, pressure and displacement measurements.