Cavitating flow in choking pipe changes violently under chocking cavitation. Using the computational fluid dynamics software of Fluent, the standard k- model and multiphase flow cavitation model, mode numerical simulation on the cavitator with choking ring under different inlet velocity and back pressure conditions, analyzed the distributions of static pressure and void ratio in cavitation area when the choking ring at different position. The results show that choking ring can prompt the back pressure of the down stream of choking cross, and the farther choking ring from the annular nozzle exit is, the more obvious the effect is. The choking ring can increase the range of optimum back-pressure generating choking cavitation, and the closer choke ring from the annular nozzle is, the pressure range of cavitating flow bigger is.