The High Sensitivity Terahertz Detection Module (HSTDM) is one of the scientific payloads of the China Space Survey Telescope. The core of the HSTDM is the NbN superconducting tunnel junction SIS (Superconductor Insulator Superconductor) mixer, operating at temperature 10 K. The installation structure of the superconducting SIS mixer needs to be specially designed to cope with the mechanical vibration during the launch phase and the thermal insulation requirements during the operation phase. Material thermal expansion characteristics investigation based on the low-temperature LVDT (Linear Variable Differential Transformer) measurement and marking scratch measurement were carried out to confirm the design validity of the thermal expansion locking mechanism. The two methods are cross-verified. The LVDT experimental measurement results show that the shrinkage rate of Teflon material changes with temperature and meets the theoretical model. At the same time, we verified the LVDT results with the marking scratch method. Consistently, the shrinkage rate of the material is 1.86% at 80 K, so the Teflon front-end locking mechanism of the superconducting SIS mixer can achieve effective separation.