The present disclosure provides an organic electroluminescent device and a manufacturing method thereof. The organic electroluminescent device includes an anode, an electron transport layer and a cathode. The material of the electron transport layer includes a mixture of a first electron transport material and a second electron transport material, the lowest unoccupied molecular orbital energy level of the first electron transport material is higher than that of the second electron transport material, and the ratio of the first electron transport material to the second electron transport material first decreases and then increases in the direction from the cathode to the anode.