讨论了光源的谱分布和线宽对无源光纤环形腔的有效精细度（线宽）的影响。对两种典型的谱分布［洛伦兹（Ｌｏｒｅｎｔｚ）和高斯（Ｇａｕｓ）］，光源给出了有效精细度（线宽）与入射光线宽之间的定量关系。分析表明：洛伦兹型光源对有效精细度（线宽）的影响比高斯型大，而且对洛伦兹型光源，有效线宽总是大于入射光的线宽 The effect of the spectral distribution and linewidth of the light source on the effective fineness (linewidth) of the annular cavity of a passive fiber is discussed. For two typical spectral distributions, Lorentz and Gauss, the light source gives the quantitative relationship between the effective fineness (linewidth) and the incident light width. The analysis shows that Lorentz type light source has a greater influence on the effective fineness (line width) than the Gaussian type, and the effective line width is always larger than the line width of the incident light for Lorentz type light sources