Aimed to intensify the ignition and combustion process of n-butane fuel in micro internal combustion (IC) engines, ignition delay characteristics of n-butane/air mixtures with tert-butyl hydroperoxide (TBHP) addition ratios below 10% were investigated numerically by CHEMKIN-PRO software. Results show that ignition delay times of n-butane can be shortened nonlinearly with TBHP addition at initial temperatures of 650 K to 1000 K, namely, the reduction rate of ignition delay times rises slowly as the TBHP addition ratio increases. In addition, the negative temperature coefficient (NTC) behavior can be weakened significantly with TBHP addition at 650 K to 1000 K. Especially, the ignition delay time of n-butane can be reduced about 32 times with 10% TBHP addition at 750 K. However, the ignition intensification effect of TBHP addition is slight when the initial temperature is above 1000 K. The acting mechanism of TBHP addition was investigated in detail by the rate of production and consumption (ROP), sensitivity, and reaction pathway analysis. The ROP analysis shows that the released and quickly consumed OH radicals with TBHP addition play an important role in promoting n-butane ignition at the lower initial temperature. However, the relatively slow consumption rate of OH radicals at higher temperature weakens the intensification effect. Furthermore, the sensitivity analysis and reaction pathway analysis indicate that the dominated elemental reactions and reaction pathway vary significantly with TBHP addition at lower initial temperature.