The toughness, as the parameter for measuring stability and vulnerability of networks, has been widely used in computer communication
networks and ontology graph structure analysis. A graph is called a fractional -critical deleted graph if after deleting any vertices from , the resulting graph is still a fractional -deleted graph. In this paper,we study the relationship between toughness and fractional -critical deleted graph. A sufficient condition for a graph G to be a fractional -critical deleted graph is determined.