Organic light emitting diodes (OLEDs) have been gradually entering the display markets and even special light area in recent years. Therefore, it is important to develop a useful simulation tool assisting in the device design of the organic materials. In the past, 1D Poisson and drift-diffusion solver have been developed by considering Gaussian-shaped density of state and Poole-Frenkel model to simulate organic materials. In this thesis, we study the method about setting up the distribution of density of state by considering the absorption spectrum of the material. The result shows that is a more appropriate method in modeling the density of state in organic materials. Moreover, 2D random dopant model is hence developed to treat the effect of random doping distribution in low doping conditions. We further calculate the 2D exciton distribution and the internal quantum efficiency (IQE) by 2D finite element method. The results show that it is consistent with experimental data.