Under the background of " dual carbon " target, higher requirements are put forward for energy saving and emission reduction of energy systems. Integrated energy system ( IES ) is the main carrier of energy system energy conservation and emission reduction. In order to deeply play the emission reduction capacity of user side and community operators in IES, this paper proposes to divide the load of user side participating in demand response into rigid load, price sensitive load and carbon price sensitive load, and add P2G equipment to community operators. On this basis, a dual-agent ladder carbon trading mechanism involving users and IES operators is established, and a two-level optimization model is established. The upper model is that the IES operator has the largest operating income, and the lower model is that the user side has the smallest energy consumption cost under the carbon price and time-sharing energy price in the park. Compared with the traditional optimization model, user side behavior is affected not only by energy prices, but also by carbon trading prices. In addition, the influence of sensitive load on demand response is analyzed, and the advantages of demand response and P2G joint optimization in energy conservation and emission reduction of IES are discussed. Finally, the effectiveness of the proposed model is verified by simulation in four situations.