This　paper　is　concerned　with　the　problem　of　robust　lagrange　stability　of　pendulum　like　systems　with　norm　constraint　structured　uncertainties.　For　the　robust　lagrange　stability　analysis　of　uncertain　pendulum　like　systems,　by　applying　the　structured　singular　value　of　a　transfer　function　to　structured　uncertainty,　a　new　frequency　domain　condition　is　obtained.　Furthermore,　based　on　the　analysis　results,　and　using　KYP　lemma,　a　dynamic　output　feedback　controller　for　the　closed　loop　systems　guaranteeing　lagrange　stability　is　designed.