The invention provides a calculation method for judging a strong or weak alternating current and direct current hybrid system in an ultra high voltage direct current hierarchical access mode. The method comprises the following steps: establishing a characteristic equation of the system according to an equivalent model of the alternating current and direct current system in the ultra high voltage direct current hierarchical access mode; providing the definitions of a hierarchical critical short circuit ratio and a hierarchical boundary short circuit ratio; calculating the critical short circuit ratio and the boundary short circuit ratio of the alternating current and direct current system; and judging that the hybrid system is strong or weak according to the relative magnitudes of the short circuit ratio, the critical short circuit ratio and the boundary short circuit ratio. The quantitative calculation method provides a good theoretical basis for stability research of the hybrid system in the ultra high voltage direct current hierarchical access mode, and has certain guiding significance for construction and operation of ultra high voltage direct current hierarchical access engineering.