Abstract: The present invention relates to a “one-pot process” for preparing intermediate of antibody-drug conjugate. The preparation process provided by the present invention is simple in operation, and needs no such steps like concentration, washing and filtration of the intermediate reaction liquid, disposal of the organic waste liquid, and packaging and storage of the intermediate. The entire reaction system comprises only one separation and purification treatment, saving costs for labor, equipment, venues, raw materials, etc., and greatly reducing the pollution to the environment. In addition, the “one-pot process” for preparing intermediate of antibody-drug conjugate of the present invention produces the intermediate of antibody-drug conjugate with higher yield. The “one-pot process” for preparing intermediate of antibody-drug conjugate provided by the present invention is more suitable for scale-up production.