High Efficiency Video Coding (HEVC) is being developed by the joint development of ISO/IEC MPEG and ITU-T Video Coding Experts Group (VCEG) and is expected to be a popular next-generation video codec in the fu-ture. HEVC can provide higher compression ratio compared to H.264/AVC standard; however, the coding complexity is dramatically increased as well. In this thesis, a fast algorithm for coding unit decision is proposed to reduce the burden of the encoding time in HEVC. The proposed algorithm exploits the temporal correlation in the neigh-boring frames of a video sequence to avoid the unnecessary examinations on CU quad-trees. In addition, based on an adap-tive threshold, the best prediction mode is early determined to SKIP mode for reducing the exhaustive evaluations at prediction stage. The performance of the proposed algorithm is verified through the test model for HEVC, HM 5.0. The experimental results show that the proposed algorithm can averagely achieve about 27%, 33%, 20%, and 21% total time encoding time reduction under Low-Delay High Efficiency, Low-Delay Low Complexity, Random-Access High Ef-ficiency, and Random-Access Low Complexity configurations respectively with a negligible degradation of coding performance. The rest of this thesis is organized as follows. Section 1 gives a brief intro-duction to the HEVC encoder, includes overview of HEVC coding standard. Simultaneously, some previously proposed methods for fast CU decision are al-so investigated in this chapter. Section 2 proposes a new early termination algo-rithm for CU decision. Section 3 demonstrates the experimental results verified through the test model for HEVC, HM 5.0 . Section 4 concludes the studies presented in this thesis.