In order to recognize Newton’s ringlike stripes more deeply, the width formulas of Newton’s ringlike stripes are derived. When refractive index N increases, the distances between the adjacent bright and dark stripes all decrease, and the reason is analyzed. The width differences between the same level bright and dark stripes corresponding to the same wavelength are studied. The law that the widths of bright and dark stripes will decrease with the increasing of the series k is proved. Two kinds of the data processing methods of double wavelengths when the curvature radius R of a plano-convex lens is measured by a sodium-vapor light are compared. And the issue how the visibility of stripes is influenced by a sodium-vapor light is discussed. Finally, the result that the corresponding series k is a function of the curvature radius R of a planoconvex lens is pointed out.