A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated.We simulate theoretically its output spectra and experimentally realize a flat-top output with a high extinction ratio.Compared to filters consisting of the conventional Panda polarization maintaining fibre,filters based on a high birefringence photonic crystal fibre loop mirror have better temperature stability.This kind of filter can be expected to be used widely in Wavelength-division-multiplexing(WDM)systems in the future.