The delay ripple of chirped FBG is analyzed in detail. A simple physical model and function of filter are set up about chirped FBG (CFBG). A numerical simulation of grating delay ripple has been done using Schrodinger equation and compared with experiment. The research shows that the system degradation depends on the period and amplitude of delay ripple. The period of CFBGs′ delay ripple is 0.01～0.1 nm indicated through a lot of experiments. The amplitude of delay ripple must be less than 15 ps in order to assure eye opening penalty less than 0.5 dB.