The invention provides a nuclear power plant system compressed air flow data validity judgment system and method. The system comprises a sampling module which is used for collecting multiple compressed air flow data sets at multiple preset time points, wherein one corresponding compressed air flow data set is collected at one preset time point, and each compressed air flow data set includes the preset number of compressed air flow data; a processing module which is used for obtaining the threshold value according to the preset number of compressed air flow data and judging the validity of thecorresponding compressed air flow data set according to the comparison result of each compressed air flow data and the threshold value and sending out an invalidity judgment signal when the processingmodule continuously judges that the two compressed air flow data sets corresponding to the two adjacent preset time points are invalid; and a control module which is used for controlling the nuclearpower plant system to stop operation when receiving the invalidity judgment signal so that the influence of data fluctuation caused by the change of the normal process state can be avoided, the sensorfault condition can be truly reflected and the misjudgment rate can be reduced.