In order to further reduce the carbon emissions of combined heat and power (CHP)-based source-load system and take into account the economic benefits, this paper improves the trading model of common stepped carbon trading, and proposes a low-carbon economic dispatching strategy of CHP-based source-load system under the interactive mechanism of green certificate and improved stepped carbon trading. The model of CHP energy system is established, the models of energy, conversion side and load side are determined, and the demand response mechanism is constructed. A two-layer scheduling model is constructed on the basis of the mathematical model. The upper layer model is an improved stepped carbon trading optimization model, and the differential evolution algorithm is used to realize the adaptive change of the stepped carbon trading parameters. Secondly, the scheduling simulation model of the lower source-load system is constructed, and the carbon trading mechanism and green certificate strategy are coupled with the operating cost of the system as the objective function to achieve direct and indirect emission reduction at the same time, and the Cplex solver is used to optimize the solution. Finally, four typical scenarios are established, and comparative analysis shows that the proposed strategies can significantly reduce carbon emissions and have good economic benefits at the same time, which can provide a reference for low-carbon economic dispatching of source-load system.