Abstract: We designed an underwater passive fluidic thrust vectoring nozzle. It can easily generate pressure difference on both sides of the primary jet to deflect the jet only by controlling the valves of the secondary flow channel. However, the nonlinear features in the control law of the thrust vectoring angle such as “sudden jump” and “hysteresis” limit the further application of this technology. In this research, the flow characteristics of the primary jet in different transverse sections of the nozzle were studied by the dye flow visualization technology and particle image velocimetry technology. We discovered flow structures such as shear layer vortices, trailing edge backflow, and separation bubbles. Three-dimensional flow structures were also observed, including the transverse flow in the near-wall region and the corner flow at the joint of two walls. The study of the interaction law between flow structures provides a physical model basis for solving the nonlinear problems such as jump and hysteresis of the thrust vectoring control law.