Due to the amount of 4K video data is large, and the traditional CPU software decoder technology cannot meet the performance requirement. The 4K video playback system based on combination of hard and soft decoding mode is designed, which uses DirectShow and CUDA hardware decoding technology. And the system includes functions of hardware system information acquisition, video source reader, video hard decoding, and video display. Experimental results show that this system can achieve good effect and greatly reduce the CPU occupancy rate when playing 4K video.