Fractionation method and system of energy-saving hydrocracking unit

In order to solve the problem of overhigh energy consumption in the fractionation process of the hydrocracking unit, the invention provides the fractionation method and system of the energy-saving hydrocracking unit, low-separated oil and hot low-separated oil respectively enter the middle part and the middle lower part of a stripping tower, and tower top light hydrocarbon, side-line fractionated oil and tower bottom heavy oil are separated out; tower bottom heavy oil enters a flash tank after passing through a heat exchanger, a top gas phase of the flash tank enters the middle of the fractionating tower, and flash tank bottom oil enters the middle-lower part of the fractionating tower after being heated by a heating furnace; the side-line fractionated oil is naphtha or naphtha and diesel oil components and enters the middle part of a fractionating tower with corresponding material properties through the side line of the stripping tower, and the temperature of the outlet of the side line of the stripping towe