Traditional researches on the stability of multicast tree mainly focuses on the dynamic change of multicast members.But in application level multicast (ALM)

where the multicast tree is constructed on end systems in the application layer

multicast members can cheat in order to improve their positions in the multicast tree

which may result in the instability of multicast tree even with stable members.This paper establishes the cheating model of ALM nodes

and discusses the instability problem of ALM tree on the occurrence of node cheating when there is no multicast member changing.The simulation results show that node cheating will bring considerable neglect impact on the stability of ALM tree.