Taking advantage of improving voltage stability L indicator, voltage level, active power loss to assess device reactive capability in overload situations. Considering the intermediate buses which connect the generator bus and load bus, the compound buses which involve the two types of buses, improving voltage stability L indicator is proposed. So device reactive capability could be calculated. The example shows the best reactive device is generator, and the second one is capacitor bank and the last one is transformer tap. Assessment of reactive device capability is beneficial and practical for operation stuff to take appropriate measures in order to transfer overload situations into normal state.