Water vapor migration driven by temperature gradients in unsaturated soils is a critical factor affecting the safety of underground nuclear waste repositories and the durability of pavements in cold regions. While some researchers have indirectly confirmed the influence of temperature gradients on water vapor circulation in confined soils, direct observational evidence has yet to be obtained. To address this gap, this paper, based on thermodynamics principles, deduces the dynamic water vapor circulation process within soil under a constant temperature gradient. Furthermore, a water vapor circulation device equipped with a specialized soil structure for head amplification was developed for direct observation. The existence of dynamic water vapor circulation was theoretically confirmed, and experimentally, the periodic changes in the water level in the piezometers were directly observed. This allows for the measurement of water vapor cycles with multiple dynamic equilibria and quantitatively reveals the laws governing water vapor circulation in open systems.