Based　on　the　theory　of　structural　dynamics,　the　solution　of　transient　vibration　under　the　input　of　sine　wave　were　deduced.　Compared　with　those　of　stable　vibration,　the　characteristics　of　the　transient　dynamic　responses　(displacement,　acceleration,　internal　force)　were　studied　in　details.　Research　results　have　shown　that　if　the　parameters　are　selected　within　a　certain　range,　the　transient　vibration　cannot　be　neglected,　and　especially,　sometimes,　the　transient　vibration　would　play　a　predominant　role　in　total　dynamical　responses.