Abstract: The disclosure provides a method for preparing drug toxin PNU-159682 (morpholinyl anthracycline derivative) for antibody-conjugated drugs and intermediates involved in the preparation method. The preparation method of the present disclosure improves the stability, practicability and scalability of the process by introducing protecting groups and changing to reagents that are capable to amplify; the preparation method of the present disclosure minimizes the risk and operational difficulty during scale-up production; production and operation is simple and convenient.