Abstract: Effects of catalyst microactivity, different distillates, catalyst to oil weight ratio, reaction temperature, and reaction time on coke formation and olefins conversion were studied in FCC naphtha olefin reformulation using a microreactor-GC on-stream analysis system and a continuous pilot riser-type FCC unit. The results showed that the formation of coke deposition and the olefins conversion took place in the transient time of the oil and the catalyst mixing and increased with the catalyst microactivity, reactants activity catalyst to oil weight ratio and reaction temperature. In the long reaction time after the oil and the catalyst mixing, the formation of coke deposition and the olefins conversion were very slow and small, and the ratio of the loss to the olefin conversion decreased, so it was favorable to increase the olefins conversion through the longer reaction time. The optimal condition for FCC naphtha olefin reformulation is reaction temperature at 390℃～440℃, catalyst to oil weight ratio 6, catalyst microactivity from 61 to 65, long reaction time, and light distillates feedstock.