Abstract: To reduce the encoding time for H.264 and apply it to the real-time practice, on the basis of the research on the block size prediction of intra frame and according to the histogram algorithm, an intra 4×4 mode or intra 16×16 mode for every macro-block are selected before coding.If the intra 4×4 prediction mode is chosen, then the fast algorithm based on the characteristic of macro-block itself is used to reduce the choices for predicted directions.Experimental results show that without the variety of PSNR, the compression time is 32.8% less than that of the original and it increases 3.2% bits rate.