Reduction stripping bleaching (soda ash 1g/L, 2g/L of sodium bicarbonate, 2-3g/L of hydrosulfite, 60℃, 30-45min, bath ratio 1:30) → pre-treatment (FeSO4, 7H2O 10g/L, 50% hypophosphorous acid 2g/L, formic acid to adjust PH = 3-3, 5, 80℃×60min) → rinsing (80℃×20min) → oxidation stripping bleaching (35% hydrogen peroxide 10mL/L, NaSiO3.5H2O 3-5g/L, 70-80℃, 45-90min, PH=8-10) → washing