Cavitation jet technology, due to its strong impact and cleaning capabilities, is widely used in cleaning and surface treatment fields. As a key component for inducing cavitation jets, the design of the cavitation nozzle is crucial. However, some researchers have focused on optimizing the central body at the axial position to improve cavitation effects, while neglecting the role of fluid near the axis. To address this issue, this study proposes a novel annular central body nozzle based on the traditional organ-pipe nozzle. The annular central body is divided into three structures: forward, reverse, and square. The variations in cavitation volume fraction, pressure, velocity, and turbulent kinetic energy are analyzed to investigate the cavitation characteristics of each new structure. Additionally, the annular central body is combined with an axial central body to further study the cavitation characteristics of the nozzle. The results show that, compared to nozzles without an annular central body, the reverse structure generates the largest cavitation area, while the square structure has the second-largest cavitation area and the highest velocity along the axis. The forward structure, due to the contraction of the jet toward the axis, reduces the overall flow velocity in the inner flow path, and the lower velocity near the wall causes a smaller low-pressure zone, leading to weaker cavitation near the wall. The inlet velocity has little impact on the shape of the cavitation cloud in the flow field but is positively correlated with the cavitation volume. Furthermore, the combination of the annular central body and the axial central body increases the cavitation cloud length, enhancing the cavitation effect behind the central body. These findings provide new theoretical support for the design and optimization of cavitation nozzles.