Abstract: The present invention belongs to the technical field of functional film materials; disclosed are a wavelength-controllable cellulose iridescent film and a method for preparation thereof. The method is: (1) mixing well a cellulose nanocrystal (CNC) suspension with lactic acid solution and glucose solution to obtain a CNC/lactic acid/glucose mixed solution; said CNC suspension being a cellulose nanocrystal suspension; (2) drying the CNC/lactic acid/glucose mixed solution to form a film to obtain a cellulose iridescent film. The method of the present invention is simple and low in cost. In the present invention, by means of the addition of lactic acid and glucose, the prepared film has iridescent film characteristics; the wavelength of the iridescent film is within the range of visible light, and the wavelengths of different colors of iridescent film are controllable.