A method for selecting the best mode of intra prediction coding for video coding applied in video coding and decoding field is provided. The method includes: constructing a rate distortion cost function based on an estimated rate to be encoded; computing the rate distortion costs for all predictive modes by using the constructed function, and selecting the predictive mode with the minimum rate distortion cost as the best mode of intra prediction coding according to the computing result. Accordingly, a device for selecting the best mode of intra prediction coding for video coding is provided. By the method, the selected mode is closer to the best mode selected by original rate distortion optimization model, thereby the need to code every block actually in the process of rate distortion optimization is effectively avoided.