Abstract: The one effect evaporator in the multi effect evaporator was simulated using the FLUENT. According to the basic structure of the designed evaporator and the actual situation of the project, the physical model was simplified reasonably and the full flow channel double flow model of the evaporator was established. Through the fluid structure coupling analysis, the flow rate and pressure characteristics of the flow field of the evaporator were mastered. The simulation results showed that the internal flow pressure loss of heat exchanger was large, the flow uniformity was unreasonable, and the liquid resistance performance was obvious; the internal liquid flow uniformity and consistency were relatively poor, and the external air flow uniformity and consistency were good. The error between experimental verification and simulation results was within the allowable range, which showed that the simulation results were reliable. In order to improve the problem of excessive pressure loss and uneven flow in the evaporator, it is necessary to optimize its internal structure reasonably.