This study designs and simulates a high-efficiency compound waste heat boiler capable of operating independently. The boiler is designed to function within a gas-steam combined cycle and can also operate independently without a gas turbine. A three-dimensional numerical model of the boiler is established using computational fluid dynamics(CFD) software to simulate its performance under three steady-state operating modes. In addition, the overall characteristics of the dynamic switching process between different modes are analyzed. The simulation results show that all three modes can meet heat load demands by adjusting the supplementary gas combustion during steady-state operation. During dynamic switching, the control method proposed in this study ensures stable operation of the waste heat boiler throughout the entire transition process. Seamless switching between the three operating modes is successfully achieved.