The experimental principle of the radius of curvature of lens by Newton’s ring and the effect of the size of dark spot in the center of Newton’s ring on the radius of curvature are discussed and analyzed. The center of different types of Newton’s ring are adjusted, the experimental data are measured and processed repeatedly. The results indicate that the lager the dark spot in the center of Newton ring, the lager the radius of curvature, furthermore, the lager the experimental error corresponding to it.