Improved embedded zero-tree wavelet (EZW for short) algorithm of dominant and subordinate pass mix-coding is presented. The subordinate pass of big coefficients that belong to a previous threshold becomes the first step during the encoding process. The dominant pass and the subordinate pass that constituted by the new big coefficients are combined to a new dominant pass. It makes encoding and decoding effective. Experimental result shows that compared to the traditional EZW

the improved algorithm can increase the peak signal to noise radio (PSNR for short) of image compression.