For video coding

the algorithm of motion estimation based on blocks is widely used. Under the prerequisite of assuring estimation accuracy

a fast classified search method applying different search range and different search steps for different blocks is given in this paper. According to the criterion of minimization of mean square error(MSE) between two frames

two threshold valuesT1andT2are determined. Each block's MSE is compared withT1andT2. Then blocks' movement is classified into fast

slow and still moving. Different search range and different search steps are applied for different blocks. For fast moving blocks three steps search is used. For slow moving blocks two steps search is used. For still blocks one step search is used. Based on the center-biased property of the motion vectors

the first and second search step use the 5×5 window and the third search step uses a 3×3 window. The results show that this method is better in quality than 3SS and reduce 3SS search steps by 23% and FS search steps by 91%. Furthermore this algorithm is more suitable for VLSI implement as well.