The evolution mechanism and characteristics of the submerged laminar round jet in a viscous homogenous shallow water layer are investigated through computational modeling.The laminar mode is used to solve the Navier-Stokes equations.In order to visualize the formation and evolution of the flow patt,the volume of fluid (VOF) method is adopted to simulate the free surface of the water layer below the air and to trace the jet fluid.The results show that the jet forms a class of quasi-two-dimensional (Q2D) vortex structures in the ambient fluid with unequal influence from the bottom wall and free surface.The time dependence of three parameters,defined for the flow patt as jet length,spiral radius and patt length,is investigated quantitatively in their non-dimensional forms.Three different Reynolds numbers and two injection durations are further considered to discuss their influence on the flow patt.