In frigid area, with heaving bottom, slope protection project will be uplifted or pushed by ice force. Thus slope protection project will be damaged. Polystyrene board can protect the soil base from the negative temperature, and improve ground temperature, minish freezing depth, weaken frost heave. Through the test of physico-mechanical and freeze-thaw properties of polystyrene board, the effect of bulk density, water content, thermal conductivity, compressive strength, frost-thaw cycle times on insulation is analyzed. At last, an anti-freezing design method of slope protection project is proposed.