In order to accurately calculate the stress and deformation of the stamping and welding impeller in the flow field, the numerical simulation of the impeller coupled system was carried out by the CAE co-simulation platform used for the multi-physical fields—ANSYS Workbench, with one-way fluid-structure interaction method. The results showed that the stress of the impeller was markedly uneven and the local stress concentration appeared in each operation condition. The total displacement of the distortion increased continuously as the radius increasing and it reached the maximum value at the edge of the impeller. The maximum equivalent stress of impeller was 48.7 MPa under the low flow rate condition of 0.6 times of design discharge, and decreased continuously as the flow rate increasing. The greatest displacement of total deformation was 0.0234 mm under low flow rate operations, which decreased firstly and then increased, and it reached the minimum value of 0.0170 mm at the larger flow rate operation of 1.2 times of design discharge. In order to enhance the reliability, the impeller should not be operated at the low flow rate condition as far as possible. The results can provide effective references to the structural design and analysis for the stamping and welding impeller.