Abstract: Sea wave motion response oi a single point moored tanker float ing production system is the prerequisite for determining the efficiency of a tanker-mounted oil gas separator. Firstly, a mechanical model was established to derive the differential equations describing its movements. Then, the forces on the tanker were analyzed by "strip theory" used in naval architecture. Inertial force, damping force, restoring force resulting from static hydraulic pressure and wave force corresponding to surge, heave, pitch were evaluated. The determination of the mooring forces on the tanker is the key to analyzing the motion response. By means of the theory of similarity, a model test was performed to determine the relation between the tension and elongation of the mooring line. A function of the tension and elastic elongation of the mooring line was obtained by polynomial regression. Then the mooring forces on the tanker could be determined. At last, taking a 11870 oil tanker converted floating production system as a example, the solution of the differential equations was obtained. A scaled model test gave identical results with the theoretical analysis.