In order to further reduce the machining cost and production time of the traditional coupling device and improve the machining quality and efficiency performance of the waterjet guided laser coupling device, a new type of coupling device with annular groove and equidistant column flow passage structure was designed according to the working principle of the waterconducting laser micromachining. A threedimensional numerical model of axially symmetrical jet water cavity was built by using SolidWorks. Numerical simulation of flow field simulation was performed using ANSYS Fluent. The internal speed vector diagram, streamline diagram, and gasliquid twophase flow simulation at the outlet of the water cavity were analyzed. The results show that the velocity vector of each plane of the waterjet guided laser coupling device is stable and tight under the conditions of an inlet diameter of 8 mm, an inlet velocity of 1 m/s, and a nozzle diameter of 0.25 mm, and the water flow at the outlet is balanced and stable and free from fluctuations. The design of the coupling device is reasonable and reliable, and it can fully meet the requirements of waterguided laser micromachining design and use.