The principle of relative stability of a dam system is the theoretical basis for planning silt-retention dams,therefore,it is of significance to study the relative stability of a dam system in planning silt-retention dams.T his paper uses Matlab 7.0-based improved BP algorithm and chaos optimization and back-propagation (COBP) model to assess the stabilities of thirteen dams in Majiagou watershed according to seven major factors affecting the stability of a dam system,i.e.dam control area,dam number,total reservoir storage,silting-allowable volume,water depth,ant-iflood capacity and silted area.Results show that seven dams out of the thirteen dams are unstable,which is confirmed by the stability coefficient analysis of each dam.The out-put of the COBP model is thus reliable.This paper further analyzes the reasons for the instabilities of seven dams and makes them stable by increasing dam height and number.All of the thirteen smal-lwatershed dams in Majiagou watershed become stable after they are replanned.This demonstrates that the COBP method has practical values in assessing the stability of a dam system.