Based　on　an　intelligent　boring　bar　containing　an　electrorheological　(ER)　fluid,　the　dynamics　of　the　cutting　system　can　be　on-line　controlled　and　varied　markedly　during　the　development　of　chatter.　In　this　paper,　the　effect　of　controllable　time　varying　dynamics　of　machine　structures　on　machining　stability　is　investigated.　A　strategy　is　proposed　to　improve　the　cutting　stability,　which　is　to　continuously　vary　resonant　frequency　of　the　cutting　system　in　process.　The　strategy　is　implemented　in　boring　by　using　the　intelligent　boring　bar,　and　the　experimental　results　are　successful.