利用太赫兹光谱技术计算物质的光学参数已成为各领域的研究重点。由于太赫兹系统以及算法提取过程依然存在缺陷，无法实现对物质光学参数的精确测量。为提高光学参数的测量准确度，对反射式太赫兹时域光谱系统进行全面的不确定度分析。首先分析了基于太赫兹反射时域光谱提取光学参数、折射率和消光系数的 7种误差来源，并分别建立了折射率和消光系数的不确定度模型；然后，以葡萄糖多晶薄片样品为例，计算其在 0.2~2.0 THz频段的折射率和消光系数的各种误差因素占综合不确定度的比例，总结误差因素对不确定度的贡献。其中，样品厚度测量的随机误差对折射率的影响最大，占总误差的 80%；传递函数误差对消光系数的影响最大，占总误差的 99%。最后，对减小折射率和消光系数的不确定度提出了建议，如采用自参考方法提取光学参数，采用智能优化算法对样品厚度和光学参数进行优化，修正 Fabry-Perot效应等。

In recent years, calculating the optical parameters of materials by using terahertz technology has become the key research in various fields. However, due to the disadvantages of the terahertz system and parameter extraction process, the accuracy of the optical parameters is far from ideal. To improve the accuracy, an overall uncertainty analysis for the Terahertz Time-Domain Reflection Spectroscopy(THz-TDS) is performed. Firstly, seven error sources of optical parameters(the refractive index and extinction coefficient) based on terahertz time-domain reflection spectroscopy are analyzed and then the models of uncertainty of refractive index and extinction coefficient are established, respectively. Secondly, the various error factors of refractive index and extinction coefficient of the polycrystalline glucose sample are analyzed. Their proportions in the combined uncertainty are estimated from 0.2 THz to 2.0 THz in order to assess their contributions to the uncertainty. The results show that the largest influence on the refractive index is the random error of sample thickness measurement with a proportion of 80%. The largest influence on the extinction coefficient is the transfer function approximation with a proportion of 99%. Finally, some suggestions for reducing the uncertainty of the refractive index and extinction coefficient are proposed such as using the self-reference method for extracting the optical parameters, using intelligent algorithm for optimizing sample thickness and optical parameters, and correcting the Fabry-Perot effect.