Based on existing blackout models and voltage steady stability theory， a new blackout model is presented. The model has the voltage steady stability analysis function module and can analyze and reveal self-organized criticality in power grid evolution from the reactive power and voltage viewpoint. The constructed voltage analysis module includes three kinds of methods: the critical voltage analysis algorithm， the reactive power and voltage mode shape algorithm based on ordinary and optimal power flow respectively， where the last algorithm is the extension of the second one， and would be more convincing in the assessment of voltage stability. Simulation on IEEE 30-bus system shows that the proposed model can practically describe the dynamics process of operation and construction of power grid， reflect totally the trend of power loss and voltage stability margin and therefore assess the level of security operation of power grid from reactive power and voltage.