The invention discloses a method, a device and a system for storing and querying data of a power network monitoring system. The method comprises the following steps: firstly, transmitting data to a plurality of computers; secondly, storing the data in a memory database of any computer; transmitting the data to another computer, meanwhile receiving the data of the other computer, storing the data in a backup database, so that the computers backup the data mutually; then, transferring the data stored in the memory database of each computer into a history database, wherein the history database is set in an independent computer; and lastly, querying corresponding data from one memory database, querying the data in the backup database if the corresponding data are unavailable in the memory database or the computer in which the memory database is positioned is powered off, and querying the data from the history database if the data are not queried in the backup database. Through adoption of the method, the device and the system, the rapid query for the data acquired by the power network monitoring system is realized; the backup database can recover the data before occurrence of an accident; monitoring data are prevented from being lost; and the data integrity of a detection system is ensured.