In order to improve the stable length of small-scale water jets, relevant software and two-phase fluid volume model were used. By setting relevant parameters, a diameter of 60 μm~100 μm of water jet was simulated on computational fluid dynamics. The effective length of water jet in different scenarios was studied. A new type of nozzle structure for actively generating a gas protective layer was designed. The results indicate that, when the nozzle diameter is 100 μm, the pressure is below 30 MPa, the traditional method of forming a contracted water jet with sharp right angles is not feasible due to the influence of machining accuracy. A relatively stable water jet at a pressure of 0.7 MPa can be generated. This method has low processing difficulty and requires low pressure, which has the reference value for the design and manufacturing of nozzle structures in water guided laser processing.