Reactive power plays an important role in power system reliability as it is closely related to system voltage stability and voltage collapse.However，the reactive power related reliability issues are seldom emphasized in conventional power reliability evaluation.This paper studies the power system reliability from the perspective of active and reactive power，respectively.Active and reactive power inadequacy and the associated voltage perturbation due to system failure are considered in reliability evaluation of power systems.A three-stage load shedding technique for past contingencies are implemented to determine the influence of active and reactive power on system reliability and to find an optimal way to relieve network violation.