The relationship between periodical fluctuation of the core diameter and srl was analyzed . the method predicting srl using core diameter data fft transform was found . the formula by shadow ' s length and shadow ' s position of two vertical directions to calculate core diameter was found 本文又推导了利用无透镜测径系统相互垂直两方向的影长和影位置信息来计算线芯直径的公式；并通过计算机仿真程序分析了该公式的误差，得到将公式误差降低到10 ~ ( - 2 )微米以下的修正方法。
