In this paper we propose dynamic manipulation for flexible object by using high speed robot arm. We consider dynamic manipulation for unknown string and describe how to manipulete it. Paticulary, we focus on the achived momentary string shapes. For example, momentary string shapes is like a J , C or d. In our strategy for dynamic manipulation of unknown string, manipulation is achieved through repeating 3steps: manipulation of string by robot arm, string parameter estimation. A string is described as the physical-dased 3D model. And ,motion data for robot arm is given as each joint angular velocity data. For simulation of motion, we input the each joint angular velocity data,and initial paramaretars of modeled string.This simulation calculate not only the motion of robot arm but also motion of modeled ropes which occured by robot motion. Parametar estimation is to string parametar by comparing image of the real manipulation with string model and motion generation by estimated model. Repeatly each step, we realize dynamic manipulation of unknown string. Finaly, we show the some experiment of dynamic manipulation ,and we demonstrate effective of parametar estimation and validity.