Sustainable reactive dyeing of cotton in green non-nucleophilic solvents was investigated. Dye fixation in the new medium was modeled using DFT calculations with the aim of understanding the role of organic bases. The novel procedure uses non-nucleophilic green solvents instead of water to eliminate the dye hydrolysis. All residuals in the spent dye bath could be conveniently recycled and reused. The three major stages in cotton reactive dyeing, cellulose swelling, dye adsorption and dye fixation were optimized respectively. Two organic bases and potassium carbonate were studied for dye fixation. The mechanisms of the amine-promoted dye fixation were modeled using density function theory (DFT) calculations. The formation of the amine-dye intermediate was elucidated and analyzed using high performance liquid chromatography (HPLC) analysis. The quaternary ammonium catalysis effect on intermediates forming was observed. A 10-cycle repeated dyeing sequence was demonstrated using Reactive orange 5 to give consistently high shade buildup, excellent colorfastness and dramatic reduction in resource consumption. The results have implications for better understanding the new hydrolysisfree and recyclable solvent dyeing process.