A method for preparing an antibody-drug conjugate (ADC). In particular, the method mainly utilizes a combination of antibody biomolecules and an ion exchange carrier through electrostatic interaction to realize solid phase preparation of an ADC drug. Elution conditions are optimized, to control a drug-to-antibody coupling ratio (DAR) and separate a polymer-coupled drug, reduce the amount of a drug used in a coupling reaction, and enhance the targeted therapeutic effect of an ADC drug. The preparation method features fewer steps, simple operation, and programmable control, facilitating industrial scale-up production, and also realizing zero retention of reducing agents and organic solvents in the preparation process, significantly improving drug safety and reducing production costs.