The invention discloses an optimal allocation method of power shortage after fault of a multi-DC sending-end grid. The method comprises the following steps: reading grid related data and carrying outanalysis and processing on the data; calculating power variation of each provincial-level control area, and judging and positioning a fault provincial-level control area; calculating actual power shortage amount of the whole grid obtained after a plurality of control measures; calculating power shortage allocation amount of each provincial-level control area and carrying out safety back calibration; if violating security constraints, calculating shortage power allocation correction of each provincial-level control area through regional equivalent power generation sensitivity; and issuing the shortage power allocation correction to each provincial-level control area in a forwarding and d remote regulating manner, and resetting to zero. The method realizes large power shortage multi-region coordinative and optimal allocation after fault and ensures quick recovery of frequency and safe and efficient operation of the multi-DC sending-end grid after disturbance by considering multi-stage scheduling and multi-class control measure action situations of the multi-DC sending-end grid after fault.