As a new video coding standard

H.264 has an enhanced motion estimation method based on block matching that each partition in an inter-coded macroblock is predicted from an area of the same size in a reference picture

the offset between the two areas(the motion vector) has 1/4-pel resolution(for the luma component).Sub-pixel motion compensation can provide significantly better compression performance than integer-pixel compensation

at the expense of increased complexity.Quarter-pixel accuracy outperforms half-pixel accuracy.Motion estimation

whose efficiency has great effect to the whole coding efficiency

is an important part during the video coding process.In this paper

we compare the basic algorithm and some fast algorithms of 1/4-pel accuracy motion estimation

then put forward a fast algorithm which use composite vector.Experiments show that this algorithm is effective.