A partition-level adaptive sub-pixel interpolation filter method for video coding is proposed in this paper. Various type of interpolation filters are exploited to compensate the limited motion accuracy represented by motion vector or improve interpolation performance of directional textures inconsistent with motion direction, an optimal filter is selected as sub-pixel interpolation filter for each macroblock partition by the principle of rate distortion optimization. The method is implemented in AVS reference software, experimental results show that by utilizing this method, the compression performance is improved up to 0.5 dB, and the decoding complexity of motion compensation is decreased up to 20%.