Abstract: Newton's rings experiment is one of the classic experiment in college physics experiments. The interference light is the two beams of the reflected light and they are not on the same line due to the refraction effect of the thin air layer. The intersection points between them and the top surface of the thin air layer are different. The maximum distance of the x coordinates between the two points is 0.30 mm and the maximum relative deviation is 1.6. It is the smaller deviation that makes the refraction effect of the thin air layer be ignored.