Automatic synthesis of optical thin films with complex spectral curve was performed using a combination of minus filters. In order to eliminate the distortion of spectral curve induced by multi-reflection among certain minus filters, a number of matching layers were interposed between the filters, and coating parameters were chosen by moans of statistical experiments. Finally, the thickness of layers for total or partial coatings were optimized by dam ping least square approach to the desired accuracy of designed curves. For example, designs of W-split coating used in colour TV cameras, visible triangular filters, wide neutral split coatings and wide band reflective coatings are given.