Abstract: In order to improve the combustion and exhaust of diesel homogeneous charge compression ignition (HCCI), a multi-zone CHEMKIN model was used to study the potential of controlling diesel HCCI combustion by blending ethanol. The effect of ethanol addition on heat release rate, the maximum pressure rise rate and the emissions were numerically calculated. The effect of ethanol addition on the active intermediate radicals OH, CH2O and H2O2 was analyzed. The results show that the ethanol addition delays the low temperature heat release (LTHR), and retards the onset of main combustion, and the maximum pressure rise rate decreases. For the ethanol with the equivalence ratio of 0.3 and blending 57% (in mol) can retard LTHR and the main combustion by about 2.4°and 6.3°, respectively. With the same equivalence ratio, the indicated mean effective pressure (IMEP) can be reduced and the maximum reduction in IMEP be achieved 11.6% by increasing the ethanol. The blending of the ethanol in diesel HCCI at high equivalence ratio offers the possibility to extend the high load limit. The ethanol addition effectively reduced the pressure rise rate and the emissions of CO and NOx.