To determine the effects of mixture concentration and fuel blending on the combustion performance of a dimethyl ether/methanol fueled HCCI engine, the combustion process under different excess air coefficients and dimethyl ether addition ratios was simulated. Parameters such as temperature, pressure, pressure rise rate and the heat release rate were examined, as well as the fuel consumption path. The results show that the peak values of the pressure, temperature, heat release rate and pressure rise rate decrease with the increase of the excess air coefficient, while the phases are delayed. Excessive excess air coefficient hinders the further oxidation reaction of CO, resulting in high CO residue. On the other hand, increasing the dimethyl ether (DME) addition ratio leads to higher peak values of pressure and temperature in the cylinder, advancing their phases, while the peak values of pressure rise rate and heat release rate decrease. The combustion heat release rate curve of dimethyl ether homogeneous charge compression ignition (HCCI) combustion exhibits three peaks. The first peak, occurring at a crane angle of 30° before topdead center (BTDC) with a temperature of 804 K, corresponds to the low-temperature-oxidation heat release of dimethyl ether. The second peak, appearing at a crane angle of 15° BTDC with a temperature of 1 193 K, corresponds to the heat release from reactions forming CO through formaldehyde and other intermediates. The third peak represents the heat release from CO oxidation when CO₂ is generated. The second and third exothermic rate peaks indicate the high-temperature oxidation exothermic stage of dimethyl ether. Additionally, when mixed with methanol, the low-temperature oxidation reaction of dimethyl ether promotes the combustion of the mixture.