An in-loop filtering acceleration circuit applied in a video codec system supporting the H.264 standard and the VC-1 standard is provided. The circuit includes multiple one-dimensional (1D) filters configured to perform a filtering process; and a filter selection unit configured to select one of the 1D filters according to the value of the boundary strength to perform the filtering processing to the reconstructed macroblock. The in-loop filtering acceleration circuit further divides the reconstructed macroblock into multiple 8×8 blocks and multiple 4×4 blocks, performs the filtering process to horizontal edges of the 8×8 blocks the reconstructed macroblock row by row from bottom to top, and performs the filtering process to horizontal edges of the 4×4 blocks row by row from top to bottom.