The　extended　synthetic　vector　method　was　applied　to　derive　an　easy-solved　mathematic　model　for　the　rotor-broken-bar　squirrel-cage　induction　motor.　Mathematical　simulations　performed　on　both　transient　and　steady　states　reveal　a　close　relationship　between　the　faulty　feature　and　parameter　setting　like　broken-bar　quantity,　broken-bar　relative　position　and　load　variation.　Simulations　and　experimental　results　indicate　that　the　maximum　value　for　faulty　feature　appears　when　the　broken-bar＇s　relative　position　spacing　in　one　pair-pole.　The　paper　theoretically　interpreted　the　phenomenon　of　no　faulty　feature　appearance　on　the　stator　current　if　specially　positioned　broken-bars.　Meanwhile,　it　revealed　the　characteristic　of　an　across　rotor　two-end-ring　phase　voltage　induced　by　the　broken-bar.　The　study　and　investigation　conclusions　are　directly　applicable　to　induction　motors　online　diagnosis　and　troubleshooting.