A novel optical dense comb filter is proposed,which is composed of many identical linearly chirped fiber Bragg gratings (LCFBG).The spectral characteristics of optical dense comb filter are numerically simulated and analyzed. The results show that the channel spacing of filter is controlled by the length of Fabry-Perot (F-P) cavity which is equal to that of unit grating. By choosing optimal structure parameters of grating,for example,the total chirp,the index modulation depth of unit grating and the concatenated grating number,the reflection spectrum of the filter shows the characteristics of high reflectivity,large bandwidth and multi-channels. For the multi-concatenated gratings,which are easy to be made with a single grating mask,the high reflection of filter can be achieved with a low index modulation depth.