Disclosed are a support method and system used after a direct-current high-power missing fault. The support method comprises the following steps of calculating an active output value which needs to beincreased before a fault is recovered after primary frequency modulation is ended by utilizing a dynamic power flow algorithm based on power grid operation data before the direct-current high-power missing fault; determining a direct-current system participating in power support according to the power grid power flow level after the primary frequency modulation is ended; and apportioning the active power output value to the direct-current system participating in support. According to the method, the non-fault direct-current power support method after the direct-current high-power missing fault is added, and the regulation means for quickly recovering the stable power grid by the regulation and control personnel are enriched.