An intra prediction method for a luma block of a video is provided. The present invention provides a solution for unifying the intra prediction of the luma block of the video, which simplifies a plurality of prediction equations defined by video standard. The predication values of common terms in the prediction equations are calculated in advance and directly selected for predicting the luma block of the video. Accordingly, only a few function parameters or register settings are needed to be modified, and then a plurality of prediction modes may use the same software function or hardware circuit to obtain the prediction values.