Power system consists of many parameter and continuously changes during the operation. The measurement data can be classified base on the operation condition. This paper proposed a voltage stability assessment in real time operation using Linear Discriminant Analysis (LDA). To identified the level of voltage stability operation, Index Stability (L-Index) has been used. The index generated from numerical calculation for steady state load flow the load adding up to the maximum load operation. However, the equation for Index calculation need a huge data of entire network system but unfortunately the data collection such measurement and communication still not sufficient to meet the requirements. In other hand, recently the advanced method to collect information with high rate data in the wide area system as known as Phasor Measurement Units (PMUs) has been widely used but the disadvantage is the location of PMU placement is limited and should be optimized due to the economic reason. To distinguish the stability level in online operation related to the index stability, Linear Discriminant Analysis has been used. The input data from limited number of PMU treated as LDA input data training and grouped it based on index calculation. This study using 14 bus IEEE system to test the propose method and the result presents the performance of the method is sufficient to measured the stability criteria in real time.