As the next generation standard of video coding, high efficiency video coding (HEVC) achieves high coding efficiency. The coding unit (CU) was adopted as the processing unit for HEVC to improve the coding efficiency. However, determining the optimal distribution of CU sizes requires lengthy calculation. To reduce the calculation time in intra prediction processing, we developed a method that determines the CU sizes using the variance value of the input image. Experimental results show that the proposed method reduces encoding time by about 40-70% compared to that of a conventional HEVC test model.