The effect of machines’ over excitation limiters may cause long-term voltage instabilities in power systems, and undervoltage load shedding is an efficient method to prevent voltage instabilities. On the basis of undervoltage load shedding using distributed controllers, this paper presents a new strategy for undervoltage load shedding based on WAMS. This strategy takes the degree of load voltage drop and the activating signal of machines’ over excitation limiters as the criterion to activate the load shedding control, and prevents the power systems from voltage collapse by repeated closed-loop load shedding. This strategy adjusts instantly according to the system’s dynamic evolution, which is of inverse-time characteristic, and it is able to protect systems from long-term voltage instabilities caused by the effect of over excitation limiters in serious fault. The simulation studies have been carried out on the modified IEEE 39 system, and results show that the proposed strategy is efficient.