In　fault　analysis　of　analog　circuits　at　subnetwork　level,　there　are　two　essential　problems:　to　determine　whether　all　the　torn　nodes　are　accessible,　and　whether　there　are　some　topological　conditions　of　the　subnetwork　which　guarantee　the　fault　at　subnetwork-level　to　be　diagnosed　correctly.　These　problems　are　solved　by　the　authors.　The　result　is　necessary　and　almost　sufficient.　If　all　torn　nodes　are　to　be　accessible,　the　required　topological　conditions　would　be　almost　satisfied　automatically.　It　is　a　special　case　of　the　authors＇　research　in　the　distribution　of　the　accessible　nodes.