The principle of using the Fabry-Perot (F-P) cavity to achieve the all-optical clock recovery is explained. Based on the reflection characteristics of the chirped fiber Bragg grating (CFBG), the wavelength selection advantage of using the chirped fiber Bragg grating to filter the signals, before using the F-P cavity to achieve the all-optical clock recovery, is analyzed theoretically. which is that the signals at the wavelength that don't require the clock recovery are filtered out by the CFBG in advance. Due to the side lobes of the CFBG reflection spectrum, the effect of the filter is not quite good, and the quality of the all-optical clock recovery is bad. So the CFBG should be apodized to get a good quality of the all-optical clock recovery.