As the new generation standard of video coding, the High Efficiency Video Coding (HEVC) is intended to provide significantly better coding efficiency than all existing video coding standards. One of his improvements is the encoding process of the structure block. It was established that this process requires high computing power because it is performed using all the possible depth levels and prediction modes to find the one with the least rate distortion (RD) cost using Lagrange multiplier. To reduce the computational complexity, fast coding unit size decision algorithms were proposed and implemented in HM. These algorithms can significantly reduce computational complexity while maintaining almost the same performance as the original HEVC encoder.