High-efficiency video coding (HEVC) is a new video coding standard being developed by the Joint Collaborative Team on Video Coding. HEVC adopted numerous new tools, such as more flexible data structure representations, which include the coding unit (CU), prediction unit, and transform unit. In the partitioning of the largest coding unit (LCU) into CUs, rate distortion optimization (RDO) is applied. However, the computation complexity of RDO is too high for real-time application scenarios. Based on studies on the relationship between CUs and their entropy, this paper proposes a fast algorithm based on entropy to partition LCU as a substitute for RDO in HEVC. Experimental results show that the proposed entropy-based LCU partition algorithm can reduce coding time by 62.3% on average, with an acceptable loss of 3.82% using Bjøntegaard delta rate.