Abstract: In order to optimize the key structure of a gas-liquid two-phase micro-nano bubble generator,a three-dimensional model of the generator was established and theits principle of the generator was analyzed. The finite element simulation software FLUENT iwas used to simulate the flow field of the generator under different working pressures. The simulation results show that , when the inlet pressure is 1.5MPa, the generator can generate the largest number of bubbles generated when the inlet pressure of the generator is 1.5MPa is t. he most and wWhen the inlet pressure of the generator is 0.5，1.0，1.5 and 2.0 MPa , respectively， the proportion of bubbles with diameters around 1nm is 41.9%，53.3%，73.2% and 69.6% respectively. The influence of the size of 4 key structures，, the diameter of flow chamber，, the large/small diameter of the expansion chamber and the diameter of the swirl chamber， on the diameter and quantity of the bubble was explored，and , and the reason of the related influence was analyzed. The results show that , when the inlet pressure is 1.5 Mpa，the micro-nano bubble generator produces the largest number of micro-nano bubbles and the most uniform particle size. Appropriately increasing the diameter of flow chamber and the diameter of the swirl chamber is beneficial to improvefor the performance of the micro-nano bubble generator，, and changing the large/small diameter of the expansion chamber has no significant effect on improving its performance.

Key words: micro-nano bubble, bubble generator, structural optimization, optimum working pressure