NOVELTY - Fuming sulfuric acid is slowly added to resorcinol, sulfonation reaction is carried out, then nitration is carried out using concentrated nitric acid, water is added to reaction system, hydrolyzed and two sulfo groups are removed from obtained 2-sulfo-4,6-dinitroresorcinol. Obtained 4,6-dinitroresorcinol is dissolved in organic solvent, reduction process is performed in hydrazine hydrate/noble metal catalyst reduction system, and then excess concentrated hydrochloric acid is added to system in drops, to obtain 4,6-diaminoresorcinol dihydrochloride crystals precipitate.    USE - Synthesis of 4,6-diaminoresorcinol dihydrochloride (claimed).    ADVANTAGE - The 4,6-diaminoresorcinol dihydrochloride having purity of 99.6% is synthesized under mild reaction condition by simple, economical and environmentally-friendly method, with reduced usage amount of noble metal catalyst, yield of 64% and nitrogen gas and water as reaction by-products.    DETAILED DESCRIPTION - Fuming sulfuric acid is slowly added into resorcinol, sulfonation reaction is carried out at 90-120 degrees C to obtain 2,4,6-trisulforesorcinol, nitration is then carried out at 10-20 degrees C using concentrated nitric acid to obtain 2-sulfo-4,6-dinitroresorcinol, water is added to reaction system to adjust mass fraction of sulfuric acid to 40-70%, hydrolyzed, and two sulfo groups are removed from 2-sulfo-4,6-dinitroresorcinol is removed, to obtain 4,6-dinitroresorcinol. The 4,6-dinitroresorcinol is dissolved in organic solvent, reduction process is performed in hydrazine hydrate/noble metal catalyst reduction system at 50-70 degrees C, and then excess concentrated hydrochloric acid is added to the system in drops, to obtain 4,6-diaminoresorcinol dihydrochloride crystals precipitate. The concentration of fuming sulfuric acid is 20-40 %mass based on free sulfur trioxide content. The mass ratio of free sulfur trioxide content in fuming sulfuric acid and resorcinol is 3:1-5:1. The molar ratio of concentrated nitric acid and resorcinol is 2 or less:1. The hydrazine hydrate/noble metal catalyst reduction system is obtained from hydrazine hydrate and noble metal catalyst composition. The molar ratio of hydrazine hydrate and 4,6-dinitroresorcinol is 2:1-12:1. The amount of noble metal catalyst with respect to 4,6-dinitroresorcinol is 0.5-2.5 wt.%.