The fault clearing actions for multi-terminal high-voltage direct current（HVDC） power transmission protection system are relative to the structure of multi-terminal HVDC system. Two fault clearing actions（blocking and restart logic of line fault） are analyzed in detail for a series type and a parallel type multi-terminal HVDC system. Other fault clearing actions are also introduced. Fast retarding with setting bypass pair is a general blocking action for the series type multi-terminal HVDC system. Blocking firing pulse is a general blocking action， and inhibiting bypass pair is often used in the parallel type multi-terminal HVDC system. For the series type multi-terminal HVDC system， pole isolating is adopted instead of converter isolating. Because there are many DC lines with different voltages， it is very complex to implement restart logic for DC line to ground faults. Runback and pole balancing must be implemented in all master converters synchronously. A new fault clearing action by closing the ground return breaker is used. For a parallel type multi-terminal HVDC system， it is only to make the time of initiating restart logic and the settings of restart logic almost identical in all converters. Decreasing DC current and blocking is a new fault clearing action. A new fault clearing action named opening DC line breaker is to isolate a faulted DC line.