E-beam lithography simulation is one of the effective tools for understanding the complex e-beam lithography process. In-house E-beam Lithography Simulator, ELIS, has been developed in order to analyze the mask CD errors. ELIS adopts the Monte Carlo method to accurately describe the electron scattering and energy deposition on the resist, and fits this result with more than two Gaussians to convolute with pattern shape efficiently and rapidly. This simulator provides the function of the proximity effect correction (PEC) and fogging effect correction. ELIS, moreover, can simulate the post exposure bake step (PEB), therefore, latent image and resist profile is given for chemically amplified resists (CAR). From the exposure simulation with ELIS, the amoung of CD variation regarding different density patterns in various conditions can be predicted. The simulation results are matched with experimented values within 5% error. Even though PEC corrects perfectly, the non-zero mean-to-target (MTT) induces the CD error. The CD errors with dose modulation and GHOST along with the MTT variation have been studied with ELIS. Also, we show these errors increasing after applying fogging effect correction.