The invention discloses a subsynchronous oscillation damping control system in a redundancy structure. Two sets of subsynchronous oscillation damping controllers and two sets of electric power electronic power units are configured, the two sets of subsynchronous oscillation damping controllers realize communication through a communication interface or a simulation cable, damping control signals outputted by each subsynchronous oscillation damping controller are respectively for the two sets of electric power electronic power units, the subsynchronous current is respectively outputted by the two sets of electric power electronic power units, the two sets of electric power electronic power units are respectively connected with a primary equipment side of an electric power system through a connection transformer, the subsynchronous current is inputted to the primary equipment side of the electric power system, and the two sets of subsynchronous oscillation damping controllers are mutuallystandby. The subsynchronous oscillation damping control system is advantaged in that smooth data switching is realized during switching, reliability and cost factors are both considered, relatively high comprehensive benefits can be realized, and the subsynchronous oscillation damping control system has excellent application prospects.