A high voltage output monitoring device and system of a power battery comprises a monitoring module, a control module and a central processor module, wherein the monitoring module carries out high voltage output monitoring, pre-charge monitoring and relay switching times monitoring; the control module controls a relay switch; the central processor module carries out processing and analysis of monitor signals, packs relay state signals, sends the packed relay state signals to a battery management system (8), prognosticates a relay health condition, sends alarming signals to the battery management system (8), judges the pre-charge state, controls a high voltage system to be opened or closed, receives the control of the battery management system, and forces the high voltage system to be opened or closed. By using the monitoring device of the present invention, it is feasible to prognosticate the lift of high voltage relay, send the relay health alarm signal in real time and to avoid the relay from causing hazard when it is damaged and cannot be closed; Furthermore, it is favorable for extending the life of battery by monitoring and controlling the pre-charge state of power battery.