The 800 kt/a ethylene plant of PetroChina Sichuan Petrochemical Company is built on the basis of a 10000 kt/a oil refining project, and the patented technology of S & W Company in the United States is adopted. The project makes full use of the advantages of mutual supply of raw materials in the refining and chemical integration enterprise to produce ethylene, propylene, butadiene and other major chemical products by cracking the naphtha and topping oil from primary processing as well as the reformate refined oil, hydrocracking naphtha and liquefied gas from secondary processing. The original design feed includes hydrocracking tail oil, light naphtha, heavy naphtha and light hydrocarbon. Due to the changes in refining load and crude oil, the quality of naphtha, which is the main feed to ethylene plant, gets worse, seriously affecting the ethylene yield of the plant. From the perspective of processing efficiency, the evaluation and optimization of cracking feedstock is of great significance for improving the product yield of the plant.