An alarming method for a railway monitoring system based on conditional expressions, comprising: normalizing all monitoring values, so as to obtain a device configuration file; wherein the normalizing all the monitoring values including classifying the monitoring values according to device type as a first level and according to device as a second level and according to attribute as a third level, so that each monitoring value is classified as a certain attribute of a certain device of a certain device type, wherein an attribute is a collected value for a device and has a numerical value, wherein the collected value is self-collected by the monitoring system or received by a system interface corresponding to respective device type; forming an alarm conditional expression and a restoration conditional expression according to the device configuration file, and inputting the alarm conditional expression and the restoration conditional expression into an alarm configuration file; and loading the alarm configuration file into a monitoring system, and checking whether an alarm condition is satisfied; wherein the checking whether an alarm condition is satisfied comprises checking whether the alarm condition is continuously satisfied within a configured delay time; if the alarm condition is not continuously satisfied within the configured delay time, then returning to recheck whether the alarm condition is satisfied;if the alarm condition is continuously satisfied within the configured delay time, exhibiting an alarm in the monitoring system; then checking whether alarm exhibition satisfies a restoration condition, including checking whether the restoration condition is continuously satisfied within the configured delay time; if the restoration condition is continuously satisfied within the configured delay time, canceling alarm exhibition in the monitoring system and returning to recheck whether the alarm condition is satisfied; if the restoration condition is not continuously satisfied within the configured delay time, then returning to recheck whether the restoration condition is satisfied. normalizing all monitoring values, so as to obtain a device configuration file; wherein the normalizing all the monitoring values including classifying the monitoring values according to device type as a first level and according to device as a second level and according to attribute as a third level, so that each monitoring value is classified as a certain attribute of a certain device of a certain device type, wherein an attribute is a collected value for a device and has a numerical value, wherein the collected value is self-collected by the monitoring system or received by a system interface corresponding to respective device type; forming an alarm conditional expression and a restoration conditional expression according to the device configuration file, and inputting the alarm conditional expression and the restoration conditional expression into an alarm configuration file; and loading the alarm configuration file into a monitoring system, and checking whether an alarm condition is satisfied; wherein the checking whether an alarm condition is satisfied comprises checking whether the alarm condition is continuously satisfied within a configured delay time; if the alarm condition is not continuously satisfied within the configured delay time, then returning to recheck whether the alarm condition is satisfied;if the alarm condition is continuously satisfied within the configured delay time, exhibiting an alarm in the monitoring system; then checking whether alarm exhibition satisfies a restoration condition, including checking whether the restoration condition is continuously satisfied within the configured delay time; if the restoration condition is continuously satisfied within the configured delay time, canceling alarm exhibition in the monitoring system and returning to recheck whether the alarm condition is satisfied; if the restoration condition is not continuously satisfied within the configured delay time, then returning to recheck whether the restoration condition is satisfied.