Purple sweet potato was used as the raw material to investigate the color-protecting technology and coloring in the preparation processing of purple sweet potato juice by single factor experiment and the orthogonal experiment.The study was also explored on the lightness and color differences.Three single color fixative and compound color fixative were chosen for the experiment.The effect of enzymolysis on the color of purple sweet potato juice was studied.Results indicated that ascorbic acid and citric acid had effects on enhancement and protection,and compound color fixative was bette3r than single color fixative.The compound of 0.45% ascorbic acid and 0.6% citric acid had the best effect.Enzymolysis was performed after color-protecting and an excellent sweet potato juice with attractive color,flavor and taste was prepared.