This paper presents methodology for installation of flexible underwater line structure. In the deepwater drilling, subsea oil development, deepsea mining and so on, pipes and structure are so long that the structure become so flexible. Dynamic response and deformation must be controlled during installation or operation to protect the structures from unexpected disturvances. Control method formulated in this paper was tested by basin experiment. Two actuators were used in the experiment. One is servo controlled wing-like appendage which generate variable drag force. The other one is variable buoyancy. Buoyancy is varied by chaging volume of air chamber. Ultrasound ranging sensor was used for measurement of displacement. Accuarcy of this sensor is high, less than 1 mm, and this sensor is also used as deformation sensor. Experiments were conducted for upending of TLP tendon and free fall of horizontal pipe. Tendon is suported at one end by a pin joint and dropped freely. In the free fall experiment the pipe is kept straight and horizontal.