Disclosed are an organic electroluminescent device and a preparation method thereof. The organic electroluminescent device is a top-emitting organic electroluminescent device having a reversed structure, and the preparation method is: dissolving zinc oxide with acetic acid to obtain a zinc oxide solution with a concentration of 0.3 g/ml-0.6 g/ml, adding a phthalocyanine substance in a mass of 1%-10% of the mass of the zinc oxide to obtain a mixture, spin-coating the mixture on a glass substrate (1) and then drying to obtain a cathode (2), and then preparing by vapor deposition, an electron injection layer (3), an electron transport layer (4), a luminescent layer (5), a hole transport layer (6), a hole injection layer (7) and an anode (8), successively, so as to obtain the organic electroluminescent device.