The disclosure relates to a power transmission control method and a flexible DC power transmission device. The method is applied to a flexible DC power transmission device and includes the steps of obtaining an AC voltage value at an outlet of the device and currents at a plurality of locations inside the device; if the AC voltage value is less than or equal to a voltage threshold value, determining whether the device satisfies an intra-area fault condition according to the currents at the plurality of locations; and if the device satisfies the intra-area fault condition, controlling the device not to implement a low-voltage ride-through strategy. According to the embodiment of the disclosure, it is possible to determine whether an intra-area fault occurs according to the change in the currents at the plurality of locations inside the device when the AC voltage value drops to the voltage threshold, and not to implement the low-voltage ride-through strategy when the intra-area fault is determined, so that the subarea identification of a fault of a flexible DC power transmission system can be realized and the over-current damage to internal modules of the power transmission device can be avoided.