The invention discloses a method and system for determining the maximum proportion of new energy of an ultra-high voltage direct current transmission end, and belongs to the technical field of power system operation control. The method comprises the steps of enabling an alternating current main network of an ultra-high voltage direct current transmission end alternating current system to be equivalent to an equivalent alternating current system, enabling a near-zone matched new energy unit of the ultra-high voltage direct current transmission end alternating current system to be equivalent toa near-zone equivalent new energy system, and obtaining equivalent parameters; determining the proportion of new energy in the near zone of the ultra-high voltage direct current transmission end alternating current system; determining the transient voltage rise of the ultra-high voltage direct current transmission end alternating current system according to the new energy proportion; and obtainingthe maximum proportion of the new energy of the ultra-high voltage direct current transmission end alternating current system. The method can be used for analysis and operation of an actual power grid, can simplify the analysis and calculation difficulty while guaranteeing the accuracy of a calculation result, is high in engineering applicability, and can effectively guarantee the safe and stableoperation of the power grid.