体折射率不均匀是一种常见的薄膜缺陷，其反演计算对于膜系的设计和制备都有重要影响。推导出体折射率不均匀薄膜的膜系特征矩阵，建立斜入射条件下的不均匀膜光谱特性计算的近似模型，探讨模型的计算精度和计算时间，并利用模型计算椭偏角验证模型的可行性。结果表明，斜入射条件下的不均匀薄膜模型为基于宽带光谱测量数据拟合的膜层缺陷数值反演应用提供了快速有效的方法。

Bulk inhomogeneity of refractive index is a normal kind of film defects, the reverse determination of which can be vital for the design and manufacture of coatings. The characteristic matrix of inhomogeneous thin films is derived, and an approximation model for the spectral characteristics calculation of the thin films at oblique incidence is presented using the matrix method. The calculation accuracy and time consumption of the presented approximation model are discussed in details. The effectiveness of the model is proved by calculating the ellipsometric angle. It turns out that the model for inhomogeneous films at oblique incidence presents a rapid and effective tool for the numerical optimization algorithm application into the data fitting of measured broadband spectral characteristics of actual multilayer coatings.