以陕西户县祁村明代公输堂的小木作“天宫楼阁”斗拱为研究对象，利用傅里叶变换红外光谱衰减全反射（Fourier Transform Infrared Attenuated Total Reflection，FTIR-ATR）法研究了小木作木材的化学组成和结构变化。根据朗伯-比尔定律，计算了木材中半纤维素、纤维素和木质素的留存率，并研究了木构件的腐朽程度。结果表明，利用FTIR-ATR法来定量分析木材中的各主要成分时具有检测准确、快速、无损以及数据重现性好等特点。由于长期暴露在空气中，木构件受到环境中的湿度变化、微生物、紫外线等因素的影响，导致木材中起填充和粘结作用的半纤维素已基本完全降解，木构件的强度、韧性和承载力都有所降低，因此需要对木构件进行必要的加固处理。本研究成果可以为后期的文物保护及修复工作提供可靠的数据支撑。

The Dougong of "Tiangong Pavilion" in Gongshu Hall, Qi Village, Hu County, Shaanxi Province is studied, which was made in the Ming Dynasty. Fourier transform infrared attenuated total reflection(FTIR-ATR) is used to study the changes of chemical composition and structure of the minor carpentry work. The retention rates of hemicellulose, cellulose and lignin in the minor carpentry work are calculated according to Lambert-Beer Law，and the decay degree of wood components is studied. The results show that FTIR-ATR method is accurate, rapid, nondestructive and reproducible in the quantitative analysis of the main components in wood. Due to long-term exposure to air, the wood components are affected by humidity changes, microorganisms, ultraviolet rays and other factors in the environment. The hemicellulose which is filled and bonded in the wood has been basically completely degraded. The strength, toughness and bearing capacity of wood components are reduced, so it is necessary to strengthen the wood components. The results can provide robust data support for future protection and restoration of cultural relics.