This paper describes the effect of liquid level on the flow behaviors inside the flash stage and on the evaporation performance of the MSF system. As an analytical approach, steady, two-dimensional balance equations with the standard k-epsilon turbulence model were solved along with the bubble growth/motion equations using the PSI-Cell method. Velocity and temperature distributions for the liquid phase and trajectories and sizes of bubbles could be predicted with reasonable accuracy. Calculation results showed that, as a whole, the evaporation performance improved with the lower liquid level inside the flash stage.