Abstract: To build more reasonable and scientific desired spectral function and improve the automatic design of coatings, a region was input for the wave band in which reflectance or transmittance needn't to be strict and a correct value should be input if there is a strict requirement when you input a desired spectral curve. At the same time, the construction of merit function was also improved according to different inputs. With the improved method number of layers of the designed coatings were reduced and the design time became shorter. The automatic design of coatings may be improved by adopting indistinct input method and improved merit function.