The invention discloses a method and a system for checking transient overvoltage after an ultra-high voltage direct current fault. The method comprises the following steps: determining an upper limitvalue of the transient voltage rise of the bus of a converter station after a direct current fault of an alternating current-direct current hybrid power grid; respectively acquiring the initial voltage of the bus of the converter station before the direct current fault of the alternating current-direct current hybrid power grid and the maximum transient voltage in the period of the direct currentfault under a current direct-current power level; calculating a difference value between the maximum transient voltage and the initial voltage as a current bus voltage rise value of the converter station, and comparing the current bus voltage rise value with the upper limit value of the transient voltage rise to obtain a check result; and when the check result indicates that the current bus voltage rise value of the converter station is equal to the upper limit value of the transient voltage rise, taking the current direct-current power as the maximum direct-current transmission power of the alternating current-direct current hybrid power grid under the restriction of the transient voltage rise.