Abstract: In this article the correlation between the coke formation and structural hydroxyls in NaHYzeolite was investigated by using ESRtechnique in cumcne cracking, and the following were observed.1.With the pretrcatmcnt temperature of zeolite increasing the cumcne cracking activity decreased and the coke formation declined.2.Also with the calcination time being prolonged the cumcne cracking activity decreased and the coke formation declined.3.The higher the exchange degree of zeolite, the higher the cracking activity of zeolite and the more the coke formation.The tendency of changes of both the cracking activity and the coke formation was in accordance with that of changes of the amount of the structural hydroxyls in NaHYzeolite as function of the prctrcatment temperature, time and the exchange degree of zeolite. On those results above it was concluded that the coke formation was a secondary reaction for the cracking of cumene,that is, not only the structural hydroxyls in NaHYwere active sites for the cracking, but also for the coke formation.