The invention relates to a hair dye and a preparation method thereof. The hair dye consists of two components, namely a component A and a component B. The component A consists of a dye mixture, a surfactant, a film forming agent, an alkalizer, water-soluble lanoline, water-soluble silicone oil, a humectant, an antioxidant, a heavy metal chelating agent and an essence and is prepared by the following steps of: adding water with the temperature between 45 and 55 DEG C to the film forming agent, and stirring for dissolution; adding the alkalizer, the water-soluble lanoline, the water-soluble silicone oil, the humectant, the antioxidant, the heavy metal chelating agent and the dye mixture, and stirring for dissolution; and finally adding the surfactant and the essence, stirring for dissolution, and filtering the mixture. The component B consists of hydrogen dioxide and phosphoric acid and is prepared by the following steps of: adding the hydrogen dioxide into water, and stirring for dissolution; adjusting the PH value to between 2 and 4 by using the phosphoric acid; and filtering the mixture to discharge the material. The hair dye is characterized in that: the production process is simple; the hair dye has the bubble formulation, is easy to spread uniformly and has good hair dyeing effect; and a user can optionally change the colour of the hair at home.