The invention relates to the field of high-voltage equipment state monitoring, and specially relates to a monitoring method and system, and an acquisition unit for a plug and play sensor. Self-description information of the sensor is sent to a monitoring unit through the acquisition unit, and the monitoring unit receives and stores the self-description information of the sensor to achieve plug-and-play of the sensor, and so, large configuration workload, low efficiency, and error-prone problems are solved; through configuration of the self-description information of the sensor in an electronicdata table, the scalability of the system is improved, and the condition of manual intervention is reduced when a power system online monitors that the sensor accesses to a state monitoring system; and the compatibility and the real-time performance of the monitoring system are improved through adoption of a communication mode of an HSR optical fiber ring network.