The invention relates to a method for coupling modification of LBF (low-boiling fraction) of peanut vine liquefied oil and WEO (waste engine oil). The method is characterized by comprising steps as follows: step one, preparation of the peanut vine liquefied oil; step two, extraction of the LBF of the peanut vine liquefied oil; step three, coupling modification of LBF of the peanut vine liquefied oil and the WEO; finally, modified biological oil with low viscosity, a high calorific value and excellent stability is prepared. The method is an energy conversion technology. The WEO in the coupling modification process is also taken as a raw material and a medium, mass transfer resistance can be reduced, carbon deposition is prevented, the quality and the stability of the modified oil are improved, and the WEO is not required to be removed from the modified oil after a reaction. The theoretical calorific value of the modified oil is equivalent to that of gasoline, and the modified oil is expected to replace diminishing fossil fuel.