This paper proposes the security distance and a security analysis method for active distribution network. Firstly

the concept of state distance is proposed and the security distance concept clan for active distribution network is established according to directions and length. Secondly

security distance calculation methods are discussed considering the inexistence and infinity of security distance for active distribution network. These methods can solve the security distance to positive and negative power flow boundaries. Then

a security analysis method based on the state security distance order is proposed

which finds the most dangerous and safest directions and security control plans with minimum cost. Analysis results also includes crossing boundaries

crossing points

displacement

vertical and axial crossing boundary directions

positive and negative crossing boundaries patterns and other abundant information. Lastly

proposed methods are verified by test cases

which help to develop and complete the concept of security distance for distribution system. The crossing boundaries analysis method also enriches the security analysis content in existence.