To obtain high resolution infrared image, both low photon efficiency and long wavelength of infrared light requires
enough large aperture telescope, but large aperture vacuum windows can hardly achieve high optical quality, so open
structure becomes the only viable choice for large infrared solar telescope. In addition to the effects of atmospheric
turbulence, open solar telescopes suffer from the heating of the optics by sunlight, especially primary mirror heating.
These factors cause the image to shiver and become blurred, and increase infrared observing noise. Since blowing air
across the front surface of the primary mirror doesn't have the necessary heat transfer coefficient to remove the absorbed
heat load, it must be cooled down to maintained at a temperature between 0K and 2K below ambient air temperature to
reduce the effects of turbulence. This paper will introduce some cooling methods and simulation results of primary
mirror in large infrared solar telescope. On the other hand, mirror material with nice thermal conductivity can reduce the
temperature difference between mirror surface and air, and mirror surface polishing at infrared wavelength can be
comparatively easier than at visible wavelength, so it is possible to select low cost metal mirror as primary mirror of
infrared solar telescope. To analyze the technical feasibility of metal mirror serving as primary mirror, this paper also
give some polishing results of aluminum mirror with electroless nickel coating.