A method and an apparatus for decoding a progressive joint photographic experts group (JPEG) bit stream as image data indicative of an image are disclosed. The method includes the following steps. First, the data indicative of a scan of the JPEG bit stream are received. Second, the data indicative of the scan are divided into a plurality of regions. One of the regions is then selected as a decoding region. Next, after the data indicative of the scan are decoded, the decoded coefficients produced according to the data indicative of the decoding region of the scan, and the nonzero history of decoded coefficients of the other regions produced according to data indicative of the other regions of the scan are stored in the memory. Finally, the decoded coefficients of the decoding region are outputted so as to construct a portion of the image data.