The invention relates to a method of using polyethylene imine to extract and separate phenolic substances from coal tar. The method comprises the steps that firstly, the polyethylene imine is used asan extractant, phenolic substances are extracted from the coal tar; then, low boiling point organic solvents such as ethyl ether, acetone, ethyl acetate and tetrahydrofuran are used as reverse extractants, phenolic substances are reversely extracted from the extraction solution obtained in the previous step; finally, the two liquid phases obtained from the reverse extraction are distilled, separation and recovery of the extractant and the reverse extractants are carried out, at the same time, the crude phenolic substances are obtained. The method is simple and convenient to operate, and wastewater containing phenol is not produced, the extractant is insoluble in the coal tar and does not pollute the coal tar, is non-corrosive to equipment, the phenolic substances can be separated and extracted efficiently, both the raw material extractant and the reverse extractants can be recycled, the manufacturing cost is greatly reduced, and the practical value is higher.