The purpose of this study is to investigate the hydrodynamic properties of an oyster floating raft system under environmental loadings. The floating raft system is an important facility for raising oyster in the near shore area of Tainan, Taiwan. The reasons for this kind of oyster culture being main income source for local fish farmers are as the following features: (1) low cost for the farming system, (2) easily to be installed in the field, and (3) easily to be harvested. Due to the raft structure could not withstand the impact of heavy storms; most of the oyster rafts are towed into harbor to avoid damage before the onset of typhoon. Since some unexpected violent sea states may occur and severely affect the integrity of raft system, the investigation of the hydrodynamic properties of a floating raft system is essential for oyster culture in the open sea. This study includes two parts: numerical simulation and physical modeling. In numerical simulation, a lumped mass method with a Morison type of relative motion equation are adopted to calculate the drag and inertial forces on raft components and then are equally divided to the associated nodes to form a system of motion equations based on Newton¡¦s second law. Through the fourth-order Runge-Kutta method, the dynamic performance of the oyster raft system can be obtained. To verify the numerical model, a physical model was carried out in a wave tank (35x1x1.2 m), and the results of dynamic performance of numerical model show good agreement with measurements. A case study of an in situ oyster farming system located near-shore of Tainan region is analyzed by the developed numerical model to investigate the maximum mooring tension, the optimal gap between rafts, and the required length of mooring line. These specifications are crucial to the shell fish farmers for their floating raft system to be survived in the strong currents and waves. The results showed that the optimum configuration for a raft system generated the lowest mooring tension is as the follows: the space between oyster rafts is about a length of oyster raft; the length of mooring line is three times of the water depth, which is consistent with the present practice of shell fish farmers adopting 3~4 times of water depth; the appropriate embedment anchor weight is 70 kg but the anchorage should be the type used by the farmers in Penghu county. Finally, this work intends to offer a guideline for the installation of oyster raft systems in the field, and anticipate minimizing the damage during the unexpected heavy sea states.