A preparation method of a gardenia yellow plant pigment belongs to the technical field of chemical dye. The preparation method comprises the following steps: selecting gardenia plants as raw materials, crushing the raw materials into a plant powder by a traditional Chinese medicine crusher, adding 50% ethanol solution into the plant powder, carrying out ultrasonic wave treatment on the mixture under the heating condition, extracting the natural dye, wherein the ratio of the plant powder and the solvent is 1:20; carrying out centrifugal treatment on the mixture liquid, taking supernatant to obtain dye; drying and concentrating the extracted natural dye by a rotary evaporator to produce a dye concentrate; carrying out high-speed centrifugal spray drying on the dye concentrate to produce the natural dye powder. The preparation method has features of wide resources of raw material, simple production technology and high production efficiency, and the prepared dye powder is very convenient to transport, store and produce.