The invention provides a method and device for selecting an optimal prediction mode of a chroma component and an electronic device, belonging to the technical field of video compression. The method comprises the steps of as a video encoder processes a short video, extracting a first encoding unit, calculating an optimal prediction mode of a luma component of the first encoding unit, when the division depth to which the first encoding unit belongs is not a preset maximum division depth, obtaining a first tag value, obtaining an optimal prediction mode of a luma component of a second encoding unit, and judging whether or not the optimal prediction mode of the luma component of the first encoding unit can be used as the optimal prediction mode of the chroma component of the first encoding unit based on the first tag value or the optimal prediction mode of the luma component of the second encoding unit and the first tag value. Thus, the repeated analysis process of the optimal prediction mode of the chroma component and the optimal prediction mode of the luma component is skipped, the analysis time of the optimal prediction mode of the chroma component is saved, and the efficiency andthe real-time performance of the video analysis are improved as a whole.