The invention relates to a contact agent and a method for processing heavy petroleum hydrocarbon by the use of the contact agent. The contact agent is composed of aluminium oxide and magnesium oxide. The contact agent has high coefficient of thermal conductivity and can realize a contact cracking reaction with high reaction temperature and short residence time during the process of processing heavy petroleum hydrocarbon in a fluidized bed or a riser, so as to effectively raise yield of a liquid and reduce yield of dry gas and coke.