A mathematical model of charge coupled device (CCD) illumination distribution for spatial scanning optical Fabry-Pérot (F-P) demodulation system is established, and a research on the output signal of CCD and its signal-to-noise ratio (SNR) is made. CCD illumination-distribution experiment is done using the designed demodulation module. And results show that the relative error between the experimental and calculated values of the CCD output voltage is less than 2.5%, and the change of relative error from the same pixel is less than 0.005 under different frame scan frequencies. The changing rate of SNR is different before and after 184 Hz with the change of frame scan frequency. Experiments are carried out to verify the validity of our established mathematical model.