The invention provides a determination method of rated power after an alternating current line is reconstructed into a direct current line. The method is characterized by determining line reconstruction times and a topology structure of the reconstructed direct current line; determining a direct-current unipolar rated voltage and a maximum direct current after the current alternating current line is reconstructed into the direct current line; carrying out multiplication processing on the direct-current unipolar rated voltage and the maximum direct current and carrying out weighting processing on a result after the multiplication processing so as to obtain rated power of the reconstructed direct current line, wherein weight in the weighting processing, the line reconstruction times and the topology structure of the reconstructed direct current line form positive correlation. The invention provides a set of complete rated power calculation method after the alternating current line is reconstructed into the direct current line. A direct-current rated power parameter after line reconstruction can be rapidly and high-efficiently calculated so that the calculated direct-current rated power accords with a concrete situation and is real. A theory basis can be provided for research of an initial stage of engineering.