The power grid is a important infrastructure that must be protected against potential threats because most of the economic actions rely on it. But the whole world turns to be smarter, the power grid advance to a smart grid which has better efficiency. Since smart grid involves both power system infrastructure and Information technology structure, there is more chance of rise in coming out of new attack vectors exploits increasing system difficulty. While security (against malicious attacks) is an important issue for grid operators, real-world constraints such as resource limitations necessarily force adoption of a risk management approach to the problem rather than complete elimination of all possible threats. Protective measures are usually taken based on a cost- benefit analysis balancing available defensive resources with perceived. Smart grid advancements present an uncertain level of risk to electric grid reliability.