The invention relates to a direct-current power grid converter station grounding fault ultra-high-speed protection method. A current transformer is arranged on the bridge arm of a converter in a direct-current power grid, and is used for detecting the over-current of the bridge arm and giving out alternating-current grounding fault criterion of the converter; for each converter station, a converter station alternating-current grounding fault and a direct-current line fault are distinguished according to the criterion, and whether an alternating-current grounding fault exists in the converter station or not is judged, and if the alternating-current grounding fault exists, a locking signal is sent to direct-current side protection, so that the operation of a direct current circuit breaker isavoided; meanwhile, the fault converter is locked, and the fault current is limited; a current-limiting inductor and a circuit breaker are installed in a direct-current power grid metal return line,and are used for limiting the fault current of the fault converter and cutting off a discharging loop; the metal return line direct-current circuit breaker closest to the fault converter station receives a signal and then acts, the fault current path is blocked, the alternating-current circuit breaker trips, an alternating-current path is blocked, and then all the non-fault converter stations continuously run normally.