The study of impeller strength for thermal power unit absorption tower desulphurization pump with new material was performed based on fluid-structure interaction calculation. The numerical simulation results of flow field in thermal power unit absorption tower desulphurization pump under 0.8 Q operating point, 1.0 and 1.2 Q were imported to ANSYS Workbench, and the structure field of thermal power unit absorption tower desulphurization pump was studied to find the stress distribution law of impeller. In the end, the strength of impeller was checked. The results show that the stress distribution of main blades, back blades, and impeller–shroud is axial symmetrical, and the maximum equivalent stress is located in the junction between the impeller–shroud and main blade outlet, which means that this area has phenomena of stress focus. This paper was performed to provide reference and guidance for the design of thermal power unit absorption tower desulphurization pump.