NOVELTY - Preparing 1-isothiocyanato-4-methylsulfinylbutane (sulforaphane), by subjecting ground broccoli seeds or rapeseeds to enzymatic treatment, grinding, mixing with radish seed liquid, separating fat layer and skim layer suspension, fermenting skim layer suspension, subjecting residue to filter press, pumping supernatant into reverse osmosis unit, adding powdered sugar to retentate, dissolving in anhydrous methanol, concentrating, mixing with ice water, pumping into 18C silica gel filler preparative liquid chromatography column, eluting and freeze-drying concentrate.    USE - The method is useful for preparing 1-isothiocyanato-4-methylsulfinylbutane (claimed) which is used in healthcare and medicinal product industries to prevent and resist cancer.    ADVANTAGE - The method enables simple and environmentally-friendly preparation of 1-isothiocyanato-4-methylsulfinylbutane having purity of more than 98%.    DETAILED DESCRIPTION - Method for preparing 1-isothiocyanato-4-methylsulfinylbutane (sulforaphane), involves (a) taking dried radish seeds having moisture content of less than 4%, soaking the dried radish seeds in ice water in ratio of 1 kg:1-5 l, grinding the soaked seeds using rotary vane mill, and collecting liquid and crushed radish seeds, (b) taking broccoli seeds or rapeseeds, grinding the seeds, passing the ground seeds through 20-60 mesh sieve, grinding the unscreened materials, drying the ground product using fluidized bed dryer, subjecting the dried product to enzymatic treatment at 110-120 degrees C and 0.14-0.2 MPa for 3-6 minutes, inactivating enzyme, soaking obtained product in ice water in ratio of 1 kg:1-4 l, and grinding the soaked product, (c) mixing ground liquid products obtained in steps (a) and (b) in ratio of 1 l:1.5-4.5 l, grinding the mixture using colloid mill, collecting liquid, adding the liquid into disc separator, maintaining at 6000-10000 revolutions per minute (rpm), collecting fat layer and skim layer suspension, and transferring the fat layer to oil refining plant for preparing edible oil, (d) adding the skim layer suspension into fermenter, adjusting pH of the suspension to 4.5-5.5 using dilute citric acid solution, fermenting at 25-35 degrees C and 60-120 rpm for 1.5-4 hours, passing the fermented product through 160-250 mesh sieve, collecting filtrate and residue, subjecting the residue to filter press, collecting filtrate and residue, and combining filtrates to obtain fermentation broth, (e) adding fermentation broth into precipitation tank, adjusting pH of the broth to 3.5-4 using dilute hydrochloric acid, allowing to stand for 10-30 minutes, centrifuging at 12000-18000 rpm, collecting supernatant and pellets, mixing the pellets and residue obtained after filter press, and air drying the mixture to obtain feed additives, (f) pumping the supernatant obtained in step (e) into reverse osmosis unit, maintaining at less than 0.4 MPa, and collecting retentate and filtrate when concentration of sulforaphane reaches 20-30%, and (g) adding powdered sugar to the retentate obtained in step (f) in ratio of 2-5 kg:1 l, where the powdered sugar is food grade amylopectin, refined konjak powder or corn starch, stir-drying the mixture at 35-45 degrees C for 10-15 hours, and collecting sulforaphane polysaccharide powder, (h) dissolving the sulforaphane polysaccharide powder in anhydrous methanol, stirring for 20-30 minutes, filtering the mixture, concentrating the filtrate at 0.07-0.09 MPa and 35-45 degrees C, mixing concentrate having methanol concentration of 3-6% and ice water in ratio of 1 kg:5-10 l, pumping the mixture into 18C silica gel filler preparative liquid chromatography column in ratio of 1 l:50-80 kg, maintaining at 25 degrees C, where detection wavelength is 245 nm and flow rate is 700 ml/minute, gradiently eluting at 37-41 minutes, where methanol as A and ultrapure water as B as mobile phase, concentration of A is increased from 5% to 25% and B is decreased from 95% to 25% in an interval of 0-15 minutes, and concentration of A is increased from 25% to 65% and B is decreased from 75% to 35% in an interval of 15-75 minutes, concentrating the eluate at 35-45 degrees C until concentration of sulforaphane reaches 30-50 %mass, freeze-drying the concentrate at 25-45 Pa and -50 degrees C to -60 degrees C for 24-36 hours to obtain sulforaphane, and analyzing and identifying chemical structure of the sulforaphane by NMR, liquid chromatography (LC)-online and polarimeter.