The utility model discloses a multichannel TCSC additional damping control device for suppressing subsynchronous oscillation. An input signal is subjected to output component superposition processingthrough the channel suppression circuits, and then an additional control signal is generated through the trigger angle calculator and transmitted to the TCSC device. additional damping compensation isgenerated by changing equivalent reactance of the TCSC; the purpose of simultaneously suppressing a plurality of sub-synchronous oscillation modes is achieved; the device comprises a signal collector, a suppression circuit, a superimposer and a trigger angle calculator, the output end of the signal collector is connected with the suppression circuit to transmit collected input signals. The suppression circuit is provided with a plurality of channels and is connected in series between the signal collector and the superimposer in parallel. The output end of the suppression circuit is connectedwith the superimposer to transmit and process signals, the output end of the superimposer is connected with the trigger angle calculator to transmit and process output signals, and the trigger angle calculator is connected with a TCSC device through the superimposer to transmit additional control signals.