The invention relates to a polyethylene terephthalate (PET) alcoholysis method with the catalysis of a first transition series metal ionic liquid. The method is characterized by taking the first transition series metal ionic liquid as a catalyst, taking one or the mixture of several from glycol, diethylene glycol, propanediol, butanediol, pentanediol, hexanediol, 1,7-heptandiol as a solvent, and under the conditions of the catalyst amount being 0.1% to 20% of the solvent mass, the reaction temperature being 80 DEG C to 250 DEG C, the pressure being 1 atm, and the reaction time being 1 min to 9 h, carrying out alcoholysis on the polyethylene terephthalate. The method has the advantages of mild reaction condition, high speed and high efficiency, high degradation rate, high catalytic activity, good selectivity, readily releasable products, environmental protection and energy saving, etc.