A formal definition of stable peers was presented

a novel method to separate stable peers from all peers and an analysis of the session sequence of stable peers in P2P networks.This study uses the KAD

a P2P file sharing system with several million simultaneous users

as an example and draws some significant conclusions about stable peers: the stable peers is about 0.6% of all peers;the 70% of stable peers possess very long total session time ensured by a large number of sessions

and possess large difference between session time;the 30% of stable peers

whose average session time is 1.8 times of the former

possess long total session time

a small number of sessions and high availability.That these two types of stable peers can play their respective roles in constructing hierarchical P2P networks.