In this paper, ZnO nanorod film has been constructed on the OLED emission surface to investigate its light-extraction enhancement effect. Similar to the ZnO nanorods film obtained experimentally by chemical bath method, the modeled ZnO nanorod film is also granted the randomly distribution characteristics. Major attention is paid to study the effect of the orientation of the ZnO nanorods on enhancement degree of light extraction. FDTD simulations indicate that the ZnO nanorods with a randomly oblique alignment can make more light extracted outside the chip compared to the ZnO nanorods possessing the rigorously vertical alignment. This conclusion shows that excessive requirement for excellent alignment of ZnO nanorods does not make any sense in optimization of OLED light emission. This makes optimization of light emission of LED by ZnO nanorods prepared through liquid-phase method much easier to implement.