For　the　linear-quadratic　(LQ)　optimal　control　system,　a　method　is　proposed　to　choose　the　suitable　weighting　matrices　which　make　the　system　have　desired　closed　loop　poles.　The　weighting　matrices　can　be　regulated　by　the　transformation　matrices　which　are　related　to　the　desired　system　poles.　So　the　LQ　system　acquires　the　desired　dynamic　quality.　These　designs　are　based　on　the　system　normal　model.　When　perturbations　occur,　the　stability　and　desired　performance　of　the　system　are　affected　severely.　So　it　is　very　important　to　obtain　the　allowable　stable　perturbation　bounds　for　analysis　and　design　of　the　system.　In　this　paper,　a　robustness　measure　bound　is　introduced　for　the　state-feedback　system,　and　the　stable　bounds　of　the　closed　loop　system　in　the　presence　of　perturbations　are　derived.　The　stable　bounds　are　obtained　for　allowable　nonlinear　time-varying　perturbation.　In　particular,　for　linear　perturbations　the　stable　bounds　are　also　derived.　A　numerical　example　is　finally　included　to　demonstrate　the　proposed　procedure.