[Purposes] The seasonal temperature change of highway subgrade in the seasonal frozen soil area causes the upward migration of water in the subgrade, making water accumulate under the closed covering layer and resulting in the covering effect, which then induces the subgrade frost heave, melt settlement, pavement cracking, frost boiling of roads, and other engineering diseases. In order to effectively suppress the covering effect under the closed covering layer, a laboratory one-dimensional soil column test was carried out based on the climatic characteristics of the seasonal frozen soil area. [Methods] Through the design of two sets of laboratory subgrade model tests under the condition of freeze-thaw cycles, the hydrothermal variation rule in the subgrade with and without capillary blocking layer in the seasonal frozen soil area was explored, and the prevention and controlling effect of capillary blocking layer on the covering effect of highway subgrade in the seasonal frozen soil area was verified. [Findings] Under the freeze-thaw cycle conditions caused by seasonal temperature change, the volume water content of soil in the traditional shallow subgrade at a depth of 2.5 and 5.0 cm increases with the increase in the number of freeze-thaw cycles, and the maximum liquid water content increases by 5.8 percentage points, which shows obvious covering effect. The soil water content at the shallow capillary blocking layer at a depth of 2.5 cm is only 1.8 percentage points with the increase in the number of freeze-thaw cycles, and the maximum liquid water content and cumulative water content at other depths decrease slightly after the three cycles. The overall water content is much smaller than that of the subgrade without the capillary blocking layer. [Conclusions] The installation of a capillary blocking layer can significantly inhibit the increase and accumulation of water content in shallow soil under the covering layer and play an important role in maintaining the stability of the water field of subgrade soil in the seasonal frozen soil area.