Abstract: Using the self-developed one-dimensional visual horizontal freezing device, one-way horizontal freezing tests are conducted on soft clay under various temperature gradients. The development of the cryostructure in the longitudinal section of the soil is observed. The results indicate that the water migration during the horizontal freezing process induces thermal responses, including variations in the temperature, water content, pore-water pressure and soil pressure, with the temperature gradient being the primary driver of water migration. During the horizontal freezing process, bidirectional water redistribution occurs in the soil due to the gravitational effects. However, the horizontal water migration is significantly greater than the vertical one. After freezing of 120 h, the water content within the freezing zone is markedly higher than the initial water content, with the maximum often observed at 1~3 cm from the freezing front. Conversely, the water content in the unfrozen area is generally lower than the initial value, indicating the dehydration consolidation in this region. Additionally, the longitudinal section of the soft clay exhibits a distinct and pronounced cryostructure during the horizontal freezing process, primarily resulting from the increased tensile stress due to low-temperature suction and crystallization stress. Based on the shape, density and distribution characteristics of the cryostructure, it can be qualitatively categorized into whole, fibrous layered, thin layered, and thick layered structures. The findings of this study provide preliminary insights into the water-heat-force-structure response processes of soft clay during the horizontal freezing, whole, fibrous layered, thin layered, and thick layered structures providing a theoretical basis for understanding horizontal frost heave mechanisms.