Horizontal frost heave disasters frequently occur in cold-region engineering projects, making it essential to understand water migration mechanisms along horizontal directions during freezing processes. Using a selfdeveloped one-dimensional visualization horizontal freezing apparatus, unidirectional horizontal freezing tests were conducted on soft clay under varying temperature gradients, and the development process of the cryostructures was continuously observed. The results indicate that the thermal-hydraulic processes, including temperature evolution, water content variation, pore-water pressure dynamics, and soil pressure changes, demonstrate similarities to vertical freezing patterns, with temperature gradients primarily influencing the magnitude of parameter variations. Under the influence of gravity, the freezing front forms an angle with the freezing direction, attributed to differential freezing rates within soil strata. Post-freezing analysis showed dualdirectional water redistribution (horizontal and vertical), with horizontal migration dominating. Maximum water content was observed 1-3 cm from the freezing front. Distinct cryostructures formed in frozen zones were identified as products of tensile stresses generated by low-temperature suction and crystallization forces. The study highlights the coupling of water transfer, thermal changes, mechanical stresses, and structural evolution during freezing and suggests that water migration and cryostructure formation are interrelated processes. This research provides robust experimental evidence for advancing the theoretical framework of horizontal water migration mechanisms in frozen soil systems.