This invention has disclosed a method for preparation of food-grade zeaxanthin through chemical isomerizaton reaction from lutein. The technical issues to be solved in this invention are quite low product yield obtained with existing methods, need of purification treatment process, and inadaptability to industrialized production. The technical schemes of this invention are: a. Mix xanthophyll crystal or its fatty acid ester with food-grade glycol or propylene glycol, for full dissolution under 60-90.degree. C. temperature. Add organic alkali into the mixed liquor acquired from step 1, for isomerization reaction to take place under inertial environment. c. Dilute the reaction solution gained from step b with the mixed solution of deionized water and ethanol, and separate the obtained crystal with conventional separating method. d. Vacuum dries the acquired crystal from step c, to get the zeaxanthin crystal. Glycol or propylene glycol is used in this invention for isomerization reaction under inertial environment after it has fully dissolved raw material under proper temperature. The product yield is reachable to more than 60%, very adaptable to industrialized product, without the need for further purification treatment.