Abstract: In the semi-dry desulfurization process of the circulating fluidized bed， the flow field of the reactor usually affects its desulfurization efficiency. Under the condition of constant flue gas velocity in the Venturi tube， the measure for adapting to different flue gas load variation by setting bypass valves across the Venturi tube section between the reactor inlet and the diffusion section can not only optimize the flow field inside the reactor， but also improve the desulfurization efficiency. In this paper， through numerical simulation， it was concluded that， when the flue gas load of the reactor changes， the opening of the bypass valves should be no less than 50%， and the number of bypass pipelines should be no less than 2， to ensure the uniform flow field distribution in the reactor. When the flue gas load was 100%， the pressure loss of the reactor was 911 Pa. With the flue gas load decrease， the pressure loss of the empty reactor was about 500 Pa. In summary， the circulating fluidized bed reactor with a bypass through the introduction and optimized regulation of the bypass structure， can achieve uniform and stable flow fields as well as low operating pressure losses within a wide flue gas load range of 50% to 100%. This provides an effective solution for enhancing desulfurization efficiency and operational adaptability in practical engineering applications.