Effect of photo irradiation on the color change of a diarylethene polymer film was investigated. Diarylethene polymer was prepared by a radical polymerization using 1-[6′-(methacryoyloxyethyloxycarbonyl)-2′-methylbenzo[b] thiophen-3′-yl]-2-(2″-methylbenzo[b]thiophen-3″-yl) hexafluorocyclopentene (BTF6MA), styrene, and butylmethacrylate. A colorless film prepared from the diarylethene polymer turned deep red hue upon exposure to UV light. The red color was immediately bleached by a visible light. Such coloration and bleaching of the polymer film could be utilized to erasable grating patterning using a phase mask, by photoprinting with two light sources of 365 nm and 633 nm. Refractive index change of the polymer film accompanied by the photochromic absorbance change was examined. Thus reversible photo-induced refractive index change (Δn_TE) of 0.0008 was determined from the photochromic conversion, with monitoring light of 830 nm.