High-efficiency video coding (HEVC) is an international video coding standard. It can reduce bit rate by almost 50% when preceding state-of-the-art standard H.264/advanced video coding (AVC) with the same objective quality but increase about 40% encoding complexity. The computation complexity of HEVC largely relies on the inter-prediction, which consumes about 60–70% of the total encoding time. This study proposes a fast mode decision method for HEVC inter-prediction. Since current coding unit (CU) is the basic coding zone for HEVC encoding process, the authors apply the edge detection method with Sobel operator to extract the edge information inside CU. It is based on the threshold-oriented means to compare those edge values and then predict the best partition mode for this CU. Furthermore, they define a weighting factor to adopt various resolutions of test sequence from wide quarter video graphics array (WQVGA) to 1600 p. The experimental results show that the proposed algorithm can reduce computational complexity by 50% on average compared with HEVC reference software, and appear to have almost the same coding performance.