Abstract: To provide references for the design of feed water control system and the once-through steam generators, the simulation models of feed water system of Chinese demonstration fast reactor were built, and both the static and dynamic characteristics of this system were analyzed. The influence of sodium temperature at evaporator outlet and the flow deviation in primary side of each model on the work state of each model was analyzed, and the limits of these parameters were figured out. The results show that sodium temperature at evaporator outlet and the flow deviation in primary side of each model must be limited to keep each model working stably.