Abstract: Low carbon olefins and distillates are produced separately by two FCC units in Jingmen petrochemical company. In order to obtain high selectivity for low carbon olefins and liquid product of distillates at the same time respectively by the two units, the operation parameters were examined, including reaction time, ratio of catalyst to oil, and regeneration temperature. The results show that these parameters have different effect on the selectivity and distillates yield. As the reaction time prolonged, thermal cracking will increase, resulting in more dry gas and H2. Increasing the ratio of catalyst to oil is the better way to keep the propylene yield and increase the total liquid yield. The higher initial oil-catalyst contact temperature is good for low carbon olefins formation. In case of high yields of gasoline and diesel needed, the regeneration temperature must be optimized.