Abstract: Search patterns have an important influence on both searching speed and encoding quality of Block- based Motion estimation Algorithms (BMA). A fast block-based motion estimation algorithm utilizing a multi- pattern switching method is proposed, during which process a halfway stop technology and a selective search method are used to promote encoding speed. The algorithm is named Diamond-Hexagon-Square (DHS) algorithm, for a small diamond pattern is used as the initial search pattern, followed by a hexagon pattern, and a square search pattern is utilized at last for refinement. Experimental results indicate that the DHS algorithm is suitable for various video sequences with different motion contents (slow, medium and fast). It is faster than the small DIAmond search algorithm (DIA), HEXagon search algorithm (HEX), a Exhausted Search Algorithm (ESA) and Unsymmetrical-cross Multi-Hexagon-grid Search (UMHexagonS) algorithm with no obvious rate-distortion performance depravation.