Provided is a distillation column assembly combining two distillation columns used in a distillation process. The distillation column assembly is characterized in that a dividing wall column (DWC) that has one inflow point, three outflow points and an internal dividing wall and a typical distillation column that has two inflow points and two outflow points are sequentially connected to each other, and in that streams of the two outflow points of the DWC are introduced into the two inflow points of the typical distillation column. The distillation column assembly improves an existing process apparatus based on two distillation columns, so that it can be easily installed, has a high energy-saving effect, and can be applied to the case where a separation pressure difference and a utility temperature difference are great.