Water-laser coupling is a critical aspect of water-jet guided laser processing, significantly affecting both the processing efficiency and quality. To further reduce the manufacturing costs, achieve uniform distribution of the water pressure inside the cavity and stability of the jet at low inlet pressures, and improve the performance of the coupling device and the quality of water-guided laser processing, a water-laser coupling device featuring multi-level symmetric channels was designed. The flow field distribution within the coupling device was analyzed, and the velocity vectors, the streamline distribution and the shape of the water jet were obtained. Simulation results show that the velocity vector distribution in each plane of the coupling device is stable without vortex, and the jet velocity at the nozzle outlet can reach 40 m/s, with a stable length of 120 mm. The results of experimental research reveal that the water jet from the nozzle is stable with an actual stable length of 85 mm, under the conditions of the water pressure of 1.0 MPa and the nozzle diameter of 250 μm. The design of the coupling device is proven to be reasonable and meets the operational requirements of water-jet guided laser processing systems.