Abstract: A method for calculating reaction heat of catalytic cracking by typical reactions was proposed on the basis of analysis of the existed calculation methods. Chemical reactions in the reactor of fluidized catalytic cracking unit （FCCU） were divided into six kinds of typical reactions: cracking，dehydrogenation，hydrogen transfer，isomerization，coking and formation of hydrogen sulfide，so that the amount and thermal effect data of each kind of typical reaction could be used to calculate the reaction heat. The reaction heat data of six large-scale commercial FCCUs was calculated by this method and compared with calculation results of the molecular expansion method，the catalytic coke method and the heat balance method. The results show that the reaction heat calculated by the typical reaction method is 45.8% and 31.8% lower than that by the molecular expansion method and the catalytic coke method, and is 77.8% higher than that calculated by the reactor-regenerator system heat balance，but the reaction heat calculated by the heat balance method is lower than that calculated by the reactor system based on the catalyst circulation quantity of carbon difference method.

Key words: catalytic cracking, reaction heat, typical reactions, secondary reaction