Abstract: The procedure of mode checking is very complex. It costs much time for predictive-frame (P-Frame) in the encoding algorithm of H.264. In this paper, a fast mode checking algorithm is presented to reduce the complexity of mode checking procedure based on direct current (DC) coefficient by reducing the number of modes required to be checked. Experimental results show that the proposed algorithm can reduce the encoding time by 54%～74% and increase the peak signal-to-noise ratio (PSNR) by 0.05 dB～0.17 dB while incurring up to 3.14% reduction or up to 3.97% increment on the total bit rate. Application shows that its encoding speed is 25 frames per second in a video encoder with TI's TMS320DM642 for D1 video signal.