For C4 hydrocarbons from heavy oil catalytic pyrolysis, the cracking behaviours on catalyst CEP-1 and quartz sand were investigated in a confined fluidized bed reactor. C4 hydrocarbons show a good cracking ability on CEP-1, and butene is easier to convert than butane. Only at high reaction temperatures can butane present a good cracking ability. On catalyst CEP-1, C4 hydrocarbons can undergo not only cracking reactions, but also such reactions as hydrogen transfer, polymerization and aromatization. The conversion of C4 hydrocarbons thermal pyrolysis is high, indicating that free radical reactions play an important part in the secondary cracking of C4 hydrocarbons. The product yields of C4 hydrocarbons pyrolysis on quartz sand are usually lower than those on catalyst CEP-1. For both catalytic pyrolysis and thermal pyrolysis of C4 hydrocarbons, the selectivity of propene is higher than that of ethene.