The present invention relates to a trifunctional catalyst used in catalytic cracking device in petroleum refining industry and a method for preparing the same. The trifunctional catalyst of the invention comprises absorbent, cerium dioxide and vanadium pentoxide acting as oxidative catalyst and cerium oxyfluoride acting as structural promoter. The oxidative catalyst and structural promoter are dispersed over the absorbent. The absorbent is spinel-based composite oxides having a general formula of MgAl2-xFexO4.yMgO, where the x is 0.01-0.5 and y is 0.2-1.2. In the trifunctional catalyst, the raw material for forming the chemical compound containing rare-earth cerium is hamartite powder. The method for preparing the trifunctional catalyst of the invention is shown as follows: the components relating to the preparation of the finished product are dissolved or dispersed into liquid materials; then the trifunctional catalyst is obtained after the mixing, drying and calcining of such liquid materials. The trifunctional catalyst of the invention is used for highly efficient absorption and desorption of sulfoxides contained in the catalytic cracking flue gas regenerated in the process of petroleum refining, the combustion promoting of carbon monoxide and the reduction of nitrogen oxides. Furthermore, the method for preparing such trifunctional catalyst is featured for its lower cost.