The invention discloses a steady-state voltage checking method and system after an extra-high-voltage DC fault, and the method comprises the steps: taking the maximum value of a steady-state voltage of a converter station bus as a constraint condition, determining the minimum input of inductive reactive compensation of an AC system, and carrying out the reactive configuration of an AC and DC hybrid system; under the current reactive power configuration mode, calculating the difference value between the steady-state voltage of the converter station bus after the fault and the steady-state voltage fluctuation maximum value as the steady-state voltage minimum value of the converter station bus before the fault; comparing a voltage of the converter station bus under the current DC power levelwith the minimum value of the steady-state voltage of the converter station bus before the fault so as to obtain a check result; when the check result indicates that the converter station bus voltageunder the current direct-current power level is equal to the minimum value of the converter station bus steady-state voltage before the fault, taking the current DC power as the maximum DC transmission power under the constraint of the steady-state voltage. The implementation method is simple and easy to implement, and the calculation efficiency can be obviously improved.