Method for preparing gardenia blue pigment

The invention relates to a method for preparing a gardenia blue pigment. The method comprises the following steps of: 1) extracting gardenia fruit powder with 50 to 60 volume percent ethanol in an amount which is 5 to 8 times the volume of the gardenia fruit powder, filtering, and concentrating to obtain concentrated solution; 2) loading the concentrated solution to a macroporous resin column, and eluting with 25 to 35 volume percent ethanol to obtain a gardenoside crude product; 3) separating the gardenoside crude product with an alumina adsorption column to obtain gardenoside, adding cellulase, a hydrolyst and amino acid into the gardenoside for hydrolysis to obtain reactive fluid, wherein the cellulase and the amino acid are added in an amount which is 5 to 10 percent based on the weight of the gardenia fruit powder; the active concentration of the cellulase is 1 mg/ml; the hydrolyst is added in an amount which is 0.5 to 1.5 percent based on the weight of the gardenia fruit powder; the hydrolysis temperature is between 50 and 60 DEG C and the hydrolysis time is 8 to 16 hours; and 4) drying the reactive fluid to obtain the gardenia blue pigment. The method has a short production cycle, and the obtained gardenia blue pigment has bright colour and high colourity.