HCCI engines have great potentials in high efficiency with ultra-low NO and particulates emissions and high flexibility in using various fuels. They operate on the basis of auto-ignition and therefore the fuel chemical kinetic is the main ignition controller. Thus initiation of combustion is a determining parameter in the prediction of combustion behavior. The main focus of the present study is to comprehensively investigate the impact of exhaust gas recirculation, fuel reforming and compression ratio on the combustion behavior of HCCI engines using ethanol as fuel. Results show that the increase of EGR delays the ignition timing, slows down the combustion reaction rate and reduces the temperature and pressure in cylinder. Also associating with the effect of exhaust gas fuel reforming, it is shown that hydrogen in the form of reformed gas helps in lowering the intake temperature required for stable HCCI operation. Also, the addition of hydrogen advances the start of combustion in the cylinder. Consequently, it is elucidated that increasing the compression ratio results in advancing the ignition timing, decreasing the burn duration and increasing the temperature and pressure. It is worth noting that the obtained results from the present model have the great compatibility with experimental data.