Abstract: Geological hazards of landslides and collapses often occur in loess slopes of seasonal frozen soil areas when winter alternates with spring, which causes serious loss of life and property. Heifangtai loess tableland of Yongjing County in Gansu Province is a typical seasonal frozen soil area, where the loess landslides hazards occur very frequently in March. The characteristics of the freeze-thaw action and its effect on slope soil strength were analyzed through field investigation and in-situ measurement. The authors confirmed the very obvious existence of freeze-thaw cycle action in Heifangtai area, summed up the macroeconomic performance of slopes affected by the freeze-thaw action, and analyzed the variation process of ground temperature in slope surface loess affected by air temperature. On such a basis, laboratory tests of loess mechanical properties were designed. The triaxial shear strength parameters of frozen loess in different initial moistures were analyzed in comparison with things of loess. Through the direct shear tests of natural loess and saturated loess which both experienced 15 freeze-thaw cycles, the authors have reached the conclusion that the freeze-thaw action had a great effect on loess strength. The results will provide references for stability analysis of loess slope induced by the freeze-thaw action.