The invention discloses a grading-gasification moderate-circulation type chemical-power polygeneration system for gathering CO2. According to a migration law of the component of COX in a cogeneration system, composition adjustment of synthesis gas is canceled, and a CO2 separating unit is placed behind a chemical synthesis unit. A moderate-circulation mean is adopted by the chemical unreacted gas, high-efficient production of a chemical product is achieved, and the enrichment of CO2 is achieved. At the same time, according to the grading-gasification moderate-circulation type chemical-power polygeneration system for gathering CO2, the CO2 discharged from a chemical island is used for the coke-CO2 gasification in a gasification island, an oxygen gasification technique in a traditional chemical-IGCC power station is replaced, and space-division power consumption and investment are saved. Compared with a system in which composition of synthesis gas is adjusted entirely and the CO2 separating unit is placed front the chemical synthesis unit, the concentration of the CO2 before separating in the grading-gasification moderate-circulation type chemical-power polygeneration system is improved to over 50% from 35%, and the separation work of the CO2 is lowered greatly. According to the disclosed cogeneration system, the relative energy-saving rate is up to 19%-21%, and the conversed production efficiency of the chemical product is up to 70%-72%.