In order to reduce the limitation of the processing level on the performance of micro-sonic nozzles, three non-standard sonic nozzle structures including the shrink nozzle, the diffusion nozzle, and the conical Venturi nozzle are proposed. It was also analyzed respectively that how the geometry and shape of the nozzle affects flow characteristics. Numerical simulation was used to analyze the internal flow field of the nozzle whose diameter is selected from 0. 03mm to 0. 12mm. Not only the influence of the geometry of the constricted section, the throat and the diffusing section on the nozzle flow characteristics were analyzed, but also the flow characteristics of them were compared. It is found that the discharge coefficient and critical back pressure of the diffusion nozzle are superior, and the processing difficulty of this type of nozzle is the smallest. In addition, throat diameter and throat length have the greatest influence on nozzle flow characteristics. In addition, it is found that the throat diameter and the throat length have the greatest influence on the nozzle flow characteristics. The larger the throat diameter and the smaller the throat length, the larger the nozzle discharge coefficient and the critical back pressure ratio. These studies provide some reference for the development of subsequent micro-nozzles.