The colloidal crystals of SiO 2 spheres were grown in cells of different thickness. The results show that the colloidal crystal grows much quickly in 0.07 mm cell than that in 1 mm cell, and the crystal quality in 0.07 mm cell is much better than that in 1 mm cell. In ultra-thin cell, the high quality colloidal crystal can be grown with large diametrical error of the silica spheres. The band gap of the colloidal crystal in 0.07 mm cell has a red shift of 24 nm over that in 1 mm cell.