Design method for the optical thin film with digital filters method is given. The optical thin films purpose spectra transfer function is obtained by utilizing the digital filters design software. Turning the math form of optical thin film transfer matrix to the lattice digital filters, the recursive relationship between the coefficients of the transfer function is got from the purpose transfer function. The film’s refractive index of each layer fit for the purpose spectra is designed with layer-peeling method by the recursive relationship. Two examples of four layers anti-reflective and eight layers reflective films design with equal optical thickness are given by this method.