Internal Thermally Coupled Distillation Column(ITCDIC) is the research frontier of distillation energy saving . This paper investigates the principium design of ideal ITCDIC. A novel design model of ideal ITCDIC is derived

which can not only directly achieve the system characteristics and comparative characteristics with conventional distillation columns

but also be used for further control and design studies. A series of detailed operation analyses are carried out

which pave the way for further research and practice application.