To overcome the drawback of the traditional lumping method, a new method constructed from structure oriented lumping (SOL) combined with Monte Carlo (MC) to simulate the secondary reactions process of fluid catalytic cracking (FCC) gasoline was developed. The SOL method was applied to represent the feedstocks and products configuration framework; then, more than 60 item reaction rules were established to produce all the reaction networks for the secondary reactions of FCC gasoline. By integral calculating each molecule reaction probability using the MC method, the product distribution thus can be obtained. Three samples of catalytic cracking gasoline, taken from the industrial FCC units of China have been used as feedstock of the simulation to check the validity of the proposed method. Some integral properties, such as average molecular weight, element compositions, and hydrocarbon compositions were predicted. The yield of upgraded gasoline, dry gas, liquefied petroleum gas (LPG), light cycle oil (LCO), heavy oil, coke, and olefin changes with extent of reaction were also simulated with this method and the predicted results agreed well with the experimental data.