Abstract: A novel technology of energy saving in distillation process，distillation with heat exchange inside，was presented for the first time based on the second law of thermodynamics.The concept of distillation with heat exchange inside and its principle of energy conservation were elaborated.Qualitative analysis indicated that this new process was especially fit for columns with high temperature difference between top and bottom.Finding internals with good performance of heat transfer as well as of mass transfer was the key to realizing this new technology.A good kind of internal，the vertical finned tube，was recommended.An equilibrium stage model，the MESHQ equations，was established in order to calculate the process of distillation with heat exchange inside.A simplified method using PRO/Ⅱ was introduced to simulate this process conveniently.