等效折射率方法是在传统光纤理论的基础上发展而来的。阐述了等效折射率方法，利用矢量波动方程分析了微结构光纤包层空间填充基模的传播常数，以及有效折射率与波长的关系，并计算了纤芯缺陷分别为1孔、3孔、7孔时光纤的归一化频率。在传统光纤理论的基础上，通过对归一化频率的分析，讨论得出不同占空比时光纤的无尽单模区，以及单模区与多模区的特性变化，这为设计单模大模场微结构光纤提供了参考。对等效折射率方法做了进一步总结，分析了其应用优点和局限。

The development of effective index model is from the basis of conventional fiber theory. This article expounds the effective index method and applies vectorial wave equation to analyze the relationship between propagation constant and effective index of space filling mode with operation wavelength in the cladding of micro-structured optical fibers. Normalized frequency is solved when the core defect is one hole missing, three holes missing and seven holes missing respectively. On the basis of conventional fiber theory, by discussing different parameters of air holes and normalized frequency, it is shown that the limitation region and variation of endless single mode, single mode and multi-mode are obtained. They are important reference for designing single large area mode micro-structured optical fibers. The effective index model is analyzed further, and the advantage of the method and summarizing the limitation of this model are discussed.