This paper proposes a novel fast search algorithm with search direction extensible, through investigating diamond search algorithm's directivity and robustness. The proposed algorithm starts with a five-point diamond search's block matching, and decides the direction from the center check point to the least block distortion point to be the search direction. Next we continuously extend one check point and detect its block distortion until the next one check point's block distortion is larger than the current check point's. Then the current check point is declared to be the center check point, and repeat the operations. Finally we end the search when the center check point has least block distortion. The proposed algorithm's search speed can increase 1 to 2 times than diamond search's with the same video quality.