The properties of soybean water vary according to temperature. In order to compare the effects of soybean water heated to different temperatures on Xuan paper, soybean water of 25 ℃, 50 ℃, 80 ℃ and 95 ℃ respectively was prepared and applied to the surfaces of Xuan paper. Various properties of Xuan paper such as pH value, resistance to ink blending, color difference induced by thermal aging, folding resistance and tensile strength were compared before and after soybean water sizing. In addition, the influence of alum-gelatin solution and soybean water on traditional Chinese painting pigments such as scarlet red, anthocyanin and gamboge etc., were investigated in terms of color saturation and hue. The microstructure of paper fibers and chemical bonding between soybean water and paper fibers were revealed using scanning electron microscopy (SEM) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The results show that 1) Xuan paper treated with soybean water is weakly alkaline regardless of the soybean water heating temperature; 2) Xuan paper treated with soybean water of 80 ℃, 95 ℃, 50 ℃ and 25 ℃ has resistance to ink blending in descending order; 3) Xuan paper treated with either alum-gelatin solution or soybean water turns yellow during thermal aging, but yellowing is less with soybean water; 4) Xuan paper treated with heated soybean water has better performance in folding resistance and tensile strength test; 5) soybean water not only encases the fibers of Xuan paper, but also consolidates the structure by crosslinking the fibers; 6) temperature rise causes oil to separate from soybeans and polysaccharide decompose into monosaccharide; 7) soybean protein forms hydrogen bonds with paper fiber, thus improving the water resistance of paper. Therefore, soybean water could play a remarkable role in the repairing and restoration of calligraphy and painting.