This paper analyzes the mechanism of systems paralysis firstly. A new network model is built, in which the relationship between attack and protection is considered. Finally, the new model is verified and some new conclusions are got by simulation. 1) Attack capability is more important than information factor. 2) Only on the condition of certain attack capability, a small fraction of operation units randomly can prevent a combat systems network from collapsing, and a small fraction of operation units preferentially can destroy a combat systems network.