The invention provides a subsynchronous oscillation suppression device and method based on a phase-locked loop error. The subsynchronous oscillation suppression device comprises a three-phase inverter, a control module and a signal detection module, wherein a first input end of the signal detection module is used for receiving the three-phase AC voltage of a synchronizer port, a second input end is used for receiving the three-phase AC voltage of a device port, a third input end is used for receiving the three-phase AC current of the device port, a first input end of the control module is connected to a first output end of the signal detection module, a second input end of the control module is used for receiving a DC bus voltage, a third input end of the control module is connected to a third output end of the signal detection module, a fourth input end of the control module is connected to a fourth output end of the signal detection module, a fifth input end of the control module is connected with a second output end of the signal detection module, the control module is used for further adjusting electrical damping size through control of reactive current according to a phase-locked error signal obtained by the signal detection module, so that the subsynchronous oscillation of a system is suppressed.