Converting MPEG-2 8-tap discrete cosine transform (DCT) coefficients to H.264/AVC 4-tap integer transform (IT) coefficients is one of the indispensable operations for transcoding MPEG-2 to H.264 in the transform domain. Motion information in the input MPEG-2 sequence should be reused as much as possible to speed up the transcoding process. Motivated by this, we first exploits the distribution information of non-zero DCT coefficients to classify the input 8times8 DCT block into three types, then proposes a fast method to perform coefficients conversion based on the type of 8times8 DCT block. The simulation results show that the proposed method significantly reduces the computational complexity, while maintains almost the same video quality compared with the existing method. Hence, it can be efficiently used in the real time transform domain MPEG-2 to H.264 transcoding