This　paper　presented　the　dynamics　equations　of　a　3-RRS　parallel　manipulator　based　on　the　Lagrange　equation,　and　addressed　the　dynamics　characteristics　of　the　mechanism.　The　equivalent　moment　of　inertia,　driving　forces/torques　and　consumed　energy　of　the　mechanism　were　analyzed　through　an　example.　The　results　of　numerical　simulation　show　that,　for　a　given　motion,　the　configuration　has　a　significant　influence　on　the　equivalent　moment　of　inertia　and　driving　forces/torques.