The utility model discloses an isothermal double -effect concentration unit, include double -effect concentration system and flash steam compression system again, the double -effect concentration system from the upper reaches to low reaches include the concentrated tower body of head tank, preheating unit, isothermal in proper order, with body economic benefits and social benefits heater with receive the cream jar, form flash steam collection vapour chamber between concentrated tower body of isothermal and the same body economic benefits and social benefits heater, I imitates I tube side and Ieffect II tube sides is the falling film evaporation module, II imitate I tube side is the concentrated module of forced circulation. The concentrated module of integrated falling film evaporation module and forced circulation is different from the concentrated quick -witted of present function singleness, and it is concentrated quick -witted to need not to set up two kinds in the concentrated machine of falling film evaporation machine and forced circulation, saves input cost and occupation space, need not to set up the knockout drum, saves the pipeline of respectively imitating between thejourney, but and the concentrated speed of every each tube side of module independently adjust and concentrated measuring in order to adapt to different production requirements, improvement use flexibility.