To improve the coding efficiency of EZW algorithm,the interval-successive-reduction approximation quantization is adopted to simplify the coding of subordinate pass,and then the improved EZW algorithm of bit successive approximation quantization for subordinate pass is presented by combining the feature of binary-bit of the significant coefficient and the interval-successive-reduction approximation quantization.This improved approach can output the binary-bit of the data in subordinate pass list directly,which discards the fussy constructing for quantizer and simplifies the coding process.Experimental results show that the improved EZW algorithm can reduce the coding time about 20%,which proves its effectiveness.