Fan-wing thrusters are primarily used for aircraft propulsion, but their potential for underwater applications has also been demonstrated. Although many achievements have been made through experimentation, there still remains much work to be done in mechanism and hydrodynamic analyses, especially for the underwater fan-wing thruster (UFT). In this work, experiments are designed and carried out for a UFT. Both self-driving and towing experiments are conducted with a custom-made experiment device. In the self-driving experiments, vertical force and velocity are measured at different rotational speeds of the cross-flow fan. Then, for studying the hydrodynamic performance, specific towing experiments and computational fluid dynamics (CFD) simulations are carried out. Simulation results are in good agreement with the towing experiment results. On the basis of the CFD simulation results, specific unique characteristics are identified. Finally, a physical model is built and analyzed, and the mechanism and distinctive characteristics are explained by the physical model.