The invention discloses a low-carbon, energy-saving and environment-friendly after-treatment method of lycra-free pure-cotton elastic fabrics and belongs to the technical field of pure-cotton fabric after-treatment. The method includes: firstly performing desizing treatment on pure-cotton woven fabrics through desizing refining working liquor composed of biological compound enzyme and tea saponin under mild conditions; then performing bleaching treatment through low-temperature bleaching working liquor composed of Schiff alkali metal coordination compounds, peroxide and low-temperature controlled catalysts in low temperature condition; and finally treating the bleached fabrics through the liquid-ammonia mercerization technology. The low-carbon, energy-saving and environment-friendly after-treatment method is simple, comfortable in wearing, low-carbon, energy-saving, environment-friendly, high in production efficiency and applicable to industrial production, and products are elastic.