NOVELTY - Anhydrous ethanol and pure water are added into aminated modified porous starch, mixed, sodium hydroxide is dripped, reacted, mixture of 90-250 mL of carbon disulfide and 300-800 mL of anhydrous ethanol is dripped into the system, mixed, reacted at 30-45 degrees C for 16-20 hours, heated to 50 degrees C, washed using 1 %mass of hydrochloric acid, sodium hydroxide and deionized water until the solution is neutral, extracted, filtered, dehydrated the solid with acetone, and vacuum-dried at 50-60 degrees C, to obtain dithio-amino formyl-modified porous starch.    USE - Preparation of dithio-amino formyl-modified porous starch used for battery, electroplating industry and mining industry.    ADVANTAGE - The method efficiently and economically provides dithio-amino formyl-modified porous starch with excellent absorptivity.    DETAILED DESCRIPTION - Starch (in g) (100) is mixed with buffer solution (2000-12000 mL), to obtain starch slurry. Then, complex enzyme (2.5-3 weight%) is added to the starch slurry, reacted at 45-60 degrees C for 2-20 hours, sodium hydroxide (17-20 ml) is added to the reaction mixture, subjected to enzymolysis, extracted and filtered, to obtain solid and supernatant. The solid is washed using distilled water until the pH value is neutral, and vacuum-dried at 40-60 degrees C, to obtain porous starch. The water absorption rate of the porous starch is more than 1.73 g/g. The complex enzyme is obtained by mixing diastatic enzyme and alpha -amylase in mass ratio of 1:2-5. The buffer solution is prepared by mixing citric acid and disodium hydrogen phosphate in mass ratio of 1:2, adding mixture to water, stirring and adjusting pH value to 5. Diluted alkaline liquor (200-400 mL) and epoxy chloropropane (5-10 mL) are added to porous starch (100), stirred, mixed uniformly, diluted alkaline liquor (100 mL) is added to reaction mixture, reacted at 25 degrees C for 18 hours, pH is adjusted until the solution neutral, extracted, filtered, washed with water for removing chloride ions, and vacuum-dried at 80 degrees C, to obtain crosslinked porous starch having moisture content of 11%. The diluted alkaline liquor is obtained by mixing sodium hydroxide, sodium chloride and water in mass ratio of 1:12:200, and forming solution having pH of 12-14. Etherifying agent chloropropane (250-300 mL) and crosslinked porous starch (100), stirred, perchloric acid (1-2.5 mL), reacted at 80-90 degrees C for 18 hours, cooled to room temperature, extracted, filtered, washed using water, anhydrous ethanol and anhydrous methanol, dehydrated with acetone, and vacuum-dried at 50-60 degrees C, to obtain etherified porous starch. Water (750-1200 mL) and anhydrous sodium carbonate (1-2) are added to etherified porous starch (100), stirred, aminating agent (150-250 mL) is added to the reaction mixture, reacted at 40-60 degrees C for 0.5-1 hour, heated to 80 degrees C for 3 hours until the pH value is neutral, extracted, filtered, washed with de-ionized water, dehydrated with acetone, and vacuum-dried at 50-60 degrees C, to obtain aminated modified porous starch. Anhydrous ethanol (1500-3000 mL) and highly pure water (200-350 mL) into aminated modified porous starch (100) at 0 degrees C, mixed, sodium hydroxide (350-500 mL) is dripped, reacted for 2 hours, mixture of 90-250 mL of carbon disulfide and 300-800 mL of anhydrous ethanol is dripped into the system, mixed, reacted at 30-45 degrees C for 16-20 hours, heated to 50 degrees C, washed using 1 %mass hydrochloric acid, sodium hydroxide and deionized water until the solution is neutral, extracted, filtered, dehydrated the solid with acetone, and vacuum-dried at 50-60 degrees C, to obtain dithio-amino formyl-modified porous starch. An INDEPENDENT CLAIM is included for usage method of dithio-amino formyl modified porous starch, which involves mixing 0.05 g of dithio-amino formyl modified porous starch, and 50 mL of heavy metal waste water which contains 200 mg/L of heavy metal, reacting for 4 hours under pH of 5, absorbing the heavy metal in the waste water using hollow structure of dithio-amino formyl modified porous starch and grafted functional group, and then detecting. The saturated absorption amount of the copper is 93 mg/g. The saturated absorption amount of nickel, zinc and chromium is more than 80 mg/g.