Abstract: An improved fast DCT algorithm is set up to reduce the complexity of H.264integer 4×4 DCT.Since the 4×4D CT distribution does not fit Laplacian model well,three simplified blocks are defined and accordingly three coefficient models are created based on a statistical analysis.Furthermore,a fast DCT algorithm based on new models is proposed.Three butterfly algorithms are designed for those 3 simplified blocks respectively,and the complexities of the proposed algorithms are analyzed and compared.Then,a complexity scalable algorithm based on the latter is presented to adjust the 4×4D CT complexity on different platforms with limited computation resource.Simulation results show that the algorithm can control H.2644×4 DCT complexity within the target with negligible loss of encoding performance.