Abstract: The dichroic beam-splitting mirror of cubic prism is an important element to realize multispectrum in one channel. Due to polarization effect, the dichroic beam-splitting mirror of cubic prism produces a high reflection peak at the high-order doubling frequency, which influences the transmittance in short wavelength seriously. A dichroic beam-splitting mirror of cubic prism, which has high transmittance in the range of 400nm～900nm and high reflectivity at 1064nm, was designed with the dummy layer concept. A valid method to remove the frequency-doubled reflection peak is presented. A sample with good optical performance was fabricated successfully. The film system is easy to be prepared, since its structure is simple, layer number is fewer, material alternatives and process requirement are less strict.