We investigate deuterium fractionation of water ice in plotoplanetary disks irradiated by UV and X-ray from a central T Tauri star. We solve chemical rate equations with the diffusion term, mimicking the turbulent mixing in the vertical direction. Water ice near the midplane is transported to the disk surface by turbulent mixing and destroyed by photoreactions, while atomic oxygen is transported to the midplane and reform water ice and/or other molecules. At r ≥ 30 AU, the cycle decreases the D/H ratios of water ice from the initial value of ˜2 × 10-2 to 10-3-10-2 within 106 yr. The resultant D/H ratios depend on the strength of mixing and the radial distance from the central star. Our results suggest that the D/H ratio in water might be already much less than 10-2 in the early phase of the disk.