Abstract：Organ-pipe cavitation jet nozzle is a common nozzle for cavitation jet, by using its internal special structure; the nozzle generates the cavitation effect in order to improve the percussion effect of jet. Therefore, the research on the structure inside of cavitation nozzle is able improve the nozzle performance. By using multi-phase flow model to study organ-pipe cavitation nozzle, on the conditions of the outlet pressure of 2MPa, for the different inlet pressure, nozzle inner flow field is numerically calculated. The results indicate that with the normal working pressure of 8MPa, nozzle throat position locates at local low speed zone and low pressure area, and cavitation position appears at the position of throat section mutation. At the same time, in the case of the nozzle throat long diameter ratio and existing corner, the internal cavitation is studied; the following conclusions are drawn: The increase of nozzle throat long diameter larger than it is actually is equivalent to increase the low pressure area, and is helpful for the generation of cavitation; that nozzle throat reducer area exists corner would seriously affect the cavitation performance of cavitation nozzle, and the larger radius is, the bigger the critical cavitation pressure is.