A deblocking filter used in a video encoder/decoder based on a multilayer is disclosed. The deblocking filtering method includes choosing a present block and its neighboring block on which a deblocking filtering will be performed, judging whether the present block and the neighboring block have been coded by the intra BL mode, choosing a deblocking filter strength according to the result of the judgment, and performing the deblocking filtering with respect to a boundary between the present block and the neighboring block and according to the deblocking filter strength.