The invention discloses a vanadium complex based on an acenaphthene quinone diimine ligand and a preparation method and application of the vanadium complex. The structural formula of the vanadium complex is shown as the following formula I (please see the specifications for the formula). The vanadium complex based on the acenaphthene quinone diimine ligand is prepared from the acenaphthene quinonediimine ligand and VCl3 (THF)3 through a one-step reaction at the normal temperature, preparation is easy, separation is not needed in the reaction process, and the product yield is high. The vanadium complex based on the acenaphthene quinone diimine ligand has good copolymerization performance, can serve as a catalyst of an olefin polymerization reaction, and is high in catalytic activity, longin life and small in using amount, an obtained polyolefin product is high in molecular weight, narrow in molecular weight distribution, and low in branching degree, and great application prospects areachieved.