In the 14th five-year period, integrated energy system (IES) plays an important role in promoting the realization of the "dual carbon" goal. In this context, in order to further explore the environmental benefits of IES, this paper constructs an IES optimization model taking into account the tiered carbon trading and the uncertainties of renewable energy. Firstly, in typical IES infrastructure, carbon capture technology and power-to-gas equipment are introduced to decouple the two-way electrical conversion while reducing carbon dioxide emissions. Then, considering the uncertainty of market electricity price and renewable energy output, the robust coefficient is introduced to establish a robust optimization model with carbon transaction cost and operating cost as the objective function. Finally, the tiered carbon trading mechanism is introduced into the system scheduling model to analyze the impact of carbon trading price on the system operation. CPLEX solver is used to solve the system, and multiple scenarios are set for comparative analysis. An example is given to prove the effectiveness of the model in the low carbon and economic system.