Various security threats of the existing information communication network can occur in Smart Grid as ICT is combined to the existing electrical grid. In order to respond to such security threats, a security architecture design that considers the ICT aspect is necessary. This paper classifies Smart Grid into different services and draws a logical architecture for AMI, which is the closest to actual users and is one of the core services composing Smart Grid. After, based on this, the paper analyzes security threats and requirements to respond to them, and examines security mechanism and algorithm that can be applied to the Smart Grid environment. Finally, it proposes Smart Grid AMI security architecture by applying it to be able to respond to security threats and requirements.