<p>The complex flow channel structure of the water spray device in a wafer dicing machine significantly increases the complexity of the incoming flow upstream of the nozzle, adversely affecting the stability of the jet. This paper employs a numerical method that couples the RANS turbulence model with the VOF multiphase flow model to conduct a systematic numerical simulation study of the multi-jet formed by the water spray device and its internal flow field, revealing the influence mechanism of internal flow on external jet stability and clarifying the main reasons for the variations in jet stability. The study shows that vortices and backflow caused by the impact of the incoming flow at the inlet within the water spray device result in varying degrees of tangential velocity of the incoming flow through the nozzle, leading to diffusion disintegration and morphological changes of the jet. Based on this phenomenon, this paper further investigates the effects of convex, concave, and plate structures on jet stability. The results show that, compared to the original water spray device structure, changing the end face from a convex structure to a plate structure can effectively suppress the formation of vortices within the flow channel, reduce the tangential velocity of the incoming flow upstream of the nozzle, and increase the dimensions of the plate structure, which thereby reducing the average swirl number of the multi-jet from the water spray device by 50%. This indicates a significant reduction in the tangential velocity ratio, which markedly enhances the stability of the multi-jet system. This study provides an important theoretical basis for the optimization design of water spray device structures and has important reference value for improving their jet cleaning effect.</p>