In the reentry operation of deepwater riser, which connects the lower end of the riser to the blowout preventer at seabed, dynamic response and deformation of the riser need to be controlled. In deeper water, the riser becomes increasingly flexible and the manipulation of the motion of drilling vessel alone is not enough. This paper presents the basic research of the reentry of riser in deepwater by active control. The coupled governing equations for drilling vessel and riser were formulated and the PC-based reentry simulation scheme was developed. The basin experiment was carried out successfully. The coupled dynamic behaviors of the floating body and the riser model were investigated through forced oscillation test. The experimental results showed that coupled motion of floating body and deformation of riser model can be controlled sufficiently and the effectiveness of present reentry method by active control was verified. The displacement of floating body and deformation of riser model were measured by ultrasound ranging sensor and optimal control forces were generated by thrusters installed at the floating body and riser model in the experiment.