The invention relates to a carboxymethyl chitosan grafted edible pigment and a preparation method. The preparation method includes: purifying an azo edible pigment; performing acryl chlorination on the purified pigment to be in grafting reaction with amino of carboxymethyl chitosan to obtain the carboxymethyl chitosan grafted edible pigment. Sunset yellow, allure red, amaranth red and carmine red of organic azo synthetic pigments may cause damage to human health and induce canceration and even has certain genetic toxicity while natural pigments have own defects. The carboxymethyl chitosan is selected as a carrier, the azo edible pigment which is widely used is selected as a color body of a novel carrier type edible pigment, and the carrier and the color body are reasonably assembled in a same molecule, so that the objective of lowering toxicity while retaining original performance of the pigment can be achieved and reduction resistance of the edible pigment can be improved.