The invention discloses a nuclear power plant earthquake monitoring method, device and system. The earthquake monitoring method comprises the steps of when occurrence of an earthquake is monitored, acquiring free field earthquake response time-displacement data and nuclear island foundation layer earthquake response time-displacement data of a plurality of main monitoring sensors within a preset time period before a triggering moment; respectively calculating a free field earthquake response spectrum and free field standard cumulative absolute velocity, and respectively calculating a nuclear island foundation layer earthquake response spectrum and nuclear island foundation layer standard cumulative absolute velocity; and triggering shutdown when both the free field earthquake response spectrum and the free field standard cumulative absolute velocity exceed a preset shutdown threshold or both the nuclear island foundation layer earthquake response spectrum and the unclear island foundation layer standard cumulative absolute velocity exceed the preset shutdown threshold. Compared with the prior art, the earthquake reaction spectrum and the standard cumulative absolute velocity are adopted to act as parameters of earthquake impact assessment, the influence and intensity of earthquake motions can be evaluated stably and accurately, and false triggering is avoided.