Based on analysis the chemical properties of blended fiber with soybean protein, under the conditions of using 40% (V / V) nitric acid solution, temperature 70 ℃ in water bath, shaking time 40 min, for soybean protein fiber content, the difference between the value of experimental measure and theoretical analysis is less than 1% by this nitric acid test method. That completed the content test method of blended fiber with soybean protein.