This paper uses the standard k-ε model, DPM, Species Transport and Finite-Rate Chemistry model to simulate momentum, energy and composition equations of a new CFB desulfurization tower with gas bypass. The numerical simulation results agree well with the experimental results. The characteristics of desulfurization and flow resistance of two desulfurization towers are analyzed by numerical simulation, and the influence of SO2 concentration to desulfurization efficiency of bypassing desulfurization tower is also analyzed. The results show that both desulfurization and flow resistance characteristics of bypassing desulfurization tower are better than those of non-bypassing desulfurization tower. The desulfurization efficiency of bypassing desulfurization tower decreases with the increase of SO2 concentration, the desulfurization efficiency increases with the increase of the relative humidity of bypassing desulfurization tower.