Abstract: During the alumina production，it needs to keep the water and salt balance for the system all the time. Generally，the multiple-effect vacuum evaporating process is adopted and heat-exchanging equipments are mainly shell and tube exchangers，and stageⅠ always adopts 0.6 MPa new steam as heat source.The composition of sodium aluminate solution is very complicated，which contains carbonates，sulphates and so on.So during the evaporating process，the impurity will separate as the form of crystals and attach to the wall of heat-exchanging pipes to form scale.The scale will affect the evaporator′s efficiency and running rate.As heat resource，new steam is supplied by the boiler.Due to the long transport distance，steam is mostly supersaturated steam(its temperature is much higher than that of saturated steam).Though it will improve the steam transport efficiency，it aggravates the evaporator′s scaling.By systematic analysis，this paper pointed out： using the saturated steam to replace supersaturated steam as heat source of evaporator will improve the heat-exchanging efficiency and the evaporation intensity effectively，and reduce energy consumption greatly.