Effect of hydrogen addition to hydrocarbon fuels on combustion characteristics were investigated using chemical full kinetics. The changes of ignition delay time and laminar flame velocity when hydrogen is added to methane or propane fuels were calculated. The result shows that for ambient pressure condition, ignition delay time decreases corresponding to the amount of hydrogen addition. However for high pressure condition, when 10% hydrogen is added to hydrocarbon fuel, ignition delay time decreases as short as that of hydrogen itself. Laminar flame velocity increases gradually with adding hydrogen, and when more than 70% hydrogen is added, laminar flame velocity rapidly increases. Furthermore, the production rate of OH is an important factor for the change of ignition delay time and laminar flame velocity, when hydrogen is added.