A decompression system for DCT-base compressed graphic data with transparent attribute includes a memory to store a compressed graphic data and a compressed mask data; a controller to read the compressed graphic data and the compressed mask data out of the memory; a first decompressor to decompress the compressed graphic data and generate a first color space image signal; a color space transformation device to transform the first color space image signal into a second color space image signal; a special color signal storage to store a plurality of special color signals; a second decompressor to decompress the compressed mask data and generate a select signal; and a first multiplexer to select the second color space image signal or a special color signal to output based on the select signal, wherein each special color signal indicates a different level of transparent attribute.