The characteristics of HCCI engines were numerically investigated by CHEMKIN software, CHEMKIN 4.0. Cylinder temperature and pressure, ignition delay time, peak temperature and pressure, indicated work, indicated power and IMEP were performed for the analysis the HCCI combustion of Methane and Hydrogen. The natural gas can be represented as the Methane (CH4), which is the main ingredient. The simulation evaluations were done by increasing the initial concentrations of H2, changing the initial temperature (inlet temperature), or varying the equivalence ratio. The numerical simulations were accomplished using CHEMKIN Suite from Reaction Design and the results are focused on ignition time, peak temperature, and indicated power. The effect of hydrogen addition to methane increases peak temperature and pressure, decreases ignition delay time, and increases indicated power.