将格兰－汤普森棱镜两半块之间的光学胶合层作为一层薄膜，利用薄膜光学理论，分析了胶合层对棱镜透射比的影响。通过研究胶合层的厚度以及光学胶折射率对入射光在胶合界面上反射率的影响，得出了s偏振光经过格兰－汤普森棱镜后的透射比。结果表明：胶合层的厚度以及光学胶折射率对棱镜的透射比均有影响，且厚度对棱镜透射比的影响呈现周期性变化；而光学胶折射率则对透射比的振荡幅度产生影响。以长度孔径比为3的格兰－汤普森棱镜为例，光学胶折射率为1．510时，棱镜的透射比在92．5%～90．8%之间振荡；光学胶的折射率在接近e光主折射率1．475～1．495之间取值时，棱镜透射比的振荡幅度较小。这一结果有利于对格兰－汤普森棱镜性能的优化。

The cement used in Glan-Thompson prisms can be seen as a layer of thin film. The influence of the cement on the transmittance of Glan-Thompson prisms is analysed based on the optical thin film theory. The influence of thickness and the refractive index of the cement on the reflectance on the cementing surface are studied in details. The transmittance of s-polarized light out of Glan-Thompson prisms is obtained. The result shows that the transmittance of the prisms is greatly influenced by the thickness and the refractive index of the cementing layer. The influence of the thickness is periodically. When the aspect ration of the prism is 3 and the refractive index of the cement is 1.510, the transmittance of the prism is from 92.5% to 90.8%. If the refractive index of optical cement approaches the main refractive index of a light, which is from 1.475 to 1.495, the amplitude of the prisms is much smaller. The result is helpful to optimize the transmitting performance of Glan-Thompson prisms.