With the development of smart grids，a power system and its information system are going to be seamlessly integrated.Hence the quantitative vulnerability assessment for a power information system becomes an important research topic.Given this background，a quantitative vulnerability assessment method based on the adjacency matrix is developed first.The proposed method employs the transition probability to describe the characteristics of attackers at two stages，i.e.selecting the access point first，and then attacking other nodes in the network from the access point.Besides，the transfer probability index between nodes is used to describe the intelligent ability of the attacker to choose the attack node.Next，the effectiveness of the method developed is demonstrated through an established evaluation example based on the information model of a slave station of a distribution automation system.