The　condition　monitoring　and　fault　diagnosis　of　rolling　element　bearings　not　only　depend　on　fault　type　but　also　fault　severity　which　is　also　essential　for　making　proper　maintenance　decision.　Aiming　at　fault　severity　assessment　of　rolling　element　bearings,　a　new　indicator　based　on　the　bicoherence　spectrum　is　proposed.　The　quadratic　phase　coupling　(QPC)　which　is　one　of　the　most　important　nonlinear　characteristics　of　fault-related　signals　can　be　detected　by　the　bicoherence　spectrum.　The　deepening　fault　severity　usually　results　in　more　frequency　components　involving　in　coupling.　In　order　to　quantify　the　coupling　degree　which　is　closely　related　to　fault　severity,　we　choose　the　mean　value　of　the　bicoherence　spectrum　as　an　indicator.　Experiments　results　showed　that　the　quantitative　trend　prediction　of　different　fault　severities　of　bearing　is　realized.　©　JVE　INTERNATIONAL　LTD.　VIBROENGINEERING　PROCEDIA.DEC　2016.