Abstract: As an easy way to implement drag reduction, ventilated cavitation has been widely used in the development of high-speed underwater vehicles. For underwater vehicles, ventilated partial cavity exhibits complex internal turbulent flow and shedding characteristics. A numerical simulation method based on boundary data immersion method (BDIM) and two-step projection method was established, ILES (implicit large eddy simulation) was used to numerically study the ventilation partial cavity, and POD (Proper Orthogonal Decomposition) modal analysis was employed to study the shedding turbulent structures of the ventilated partial cavity. The results show that ventilation partial cavities have transparent cavity region, gas-water mixing region, shedding region and tail vortex region, in which there are complex annular vortex formation, crushing and shedding processes, which significantly affect the development of ventilation partial cavities. In the POD modal analysis, the distribution region of the main modes is highly correlated with the formation and breaking region of the annular vortex, which indicates that the foam vortex shedding of ventilation partial cavities is caused by the development and evolution of the annular vortex.