VSM (mechanical vertical machine) is a new mechanized shaft construction technology integrating the advantages of full-face milling excavation, prefabricated assembly, and automatic control. Despite recent breakthroughs in its engineering application in China, VSM technology still faces challenges such as precise posture control, dynamic adjustment of suspension forces, and prevention of difficult sinking risks, which urgently require in-depth research on the time-varying laws of its suspension characteristics and sinking posture. Based on field measurement data from a Shanghai VSM project, the coupling mechanism between suspension forces and construction posture was systematically investigated. The time-varying laws of posture changes, side resistance, and sinking speed were also fully examined through measured data analysis. The findings show as follows. The time-history curve of VSM suspension forces exhibits a “fluctuation-trend” dual-stage characteristic, with its mean value first increasing and then decreasing as depth increases. Difficulties in shaft sinking are attributed to increasing side resistance and buoyancy. High sensitivity is observed during shallow construction, while the impact is limited at greater depths. Shaft side resistance is found to be highly sensitive to dynamic inclination rates this influence is particularly high during the shallow construction phase but becomes comparatively limited as depth increases. The distribution of side friction is significantly altered by shaft inclination. Engineering practice demonstrates that controlling single sinking depth within 20 cm can effectively improve construction stability and reduce the risk of posture instability.