To　deal　efficiently　with　imprecise　and　uncertain　data　associated　with　structural　parameters　and　exciting　loads,　a　multilevel　control　method　was　presented　for　vibration　control　of　structures　based　on　phase　plane　analysis.　The　phase　plane　was　divided　into　many　local　grid　regions,　and　the　trajectory　point　corresponding　to　any　instantaneous　motion　state　of　the　controlled　mass　could　be　mapped　to　a　grid　region.　The　control　force　was　obtained　by　distinguishing　the　motion　trend　of　the　controlled　mass.　Effectiveness　of　the　proposed　algorithm　was　demonstrated　through　a　numerical　example　which　considered　a　three-storey　structure　controlled　with　the　active　tendon　system　(ATS)　installed　in　the　first　storey.　Numerical　results　show　that　the　proposed　algorithm　results　in　significant　decrease　in　the　seismic　response　of　the　structure　when　compared　to　the　uncontrolled　case,　and　the　control　performance　of　the　algorithm　is　also　superior　to　that　of　the　linear　quadratic　regulator　(LQR)　algorithm.