Carboxymethyl starch （CMS） with a degree of substitution （DS） of 0. 8901 and with a transparency of 89. 2% was synthesized from potato starch, with ethanol as the solvent. Then, the structure and morphology of potato starch and CMS were characterized by means of FT-IR and ESEM, and the effects of synthesis factors on the transparency of the CMS paste were analyzed. The results indicate that （ 1 ） the transparency of CMS paste is influenced by both the DS and the etherification uniformity; （2） after the carboxymethylation, the transparency of CMS paste increases by 53.8% and the freeze-thaw stability as well as the storage stability improves; （3） the transparency of CMS paste changes slightly in alkaline condition but gradually descends with the increase of acidity ; （4） as for the acid-resistant performance, the CMS with high DS is superior to that with low DS; and （5） as for the influences of food additives, sodium chloride and citric acid both reduce the paste transparency, while glucose and sucrose have an opposite effect.