An application of chirped fiber grating in an ultra long-hual DWDM system is presented in the paper. The interaction between the chirped fiber gratings at different wavelengths are analyzed for the first time. A method of prolonging the distance between gratings to surpass the coherent length of the light source is proposed to suppress the interaction between the gratings. By using chirped fiber gratings, we realized a transmission system of 8×10Gbit/s signal on G.652 fiber over 1500km.