The invention discloses a distribution network series capacitance compensation device and method capable of suppressing subsynchronous resonance. The series capacitance compensation device is composedof a compensation unit and a subsynchronous resonance suppression unit, wherein the compensation unit includes a capacitor, a damping circuit, a voltage limiter and a bypass circuit breaker and is used for improving the voltage quality under the continuous operating voltage; the subsynchronous resonance suppression unit includes an inductance coil, a thyristor and a control branch, and the control branch is composed of a power supply, a band-pass filter, a rectification circuit, a voltage comparator and a trigger circuit. When subsynchronous resonance occurs between the compensation unit anda distribution system, subsynchronous resonance frequency and voltage signals of the distribution network are monitored in real time, the band-pass filter carries out filtering on the signals and converts the AC signals into DC signals through the processing of the rectification circuit, the DC signals are transmitted to the voltage comparator for comparison and output to the trigger circuit for processing so as to trigger the thyristor to be reliably conducted. The power supply provides an operating power supply for the subsynchronous resonance unit.