The paper presents the Rresults of numerical analysis of the inverse effect that support struts, placed in thean exhaust diffuser, have on flow in of the "’last turbine stage – exhaust diffuser"’ section. It has been shown that in the regime with moderate flow swirl at the diffuser inlet power struts have virtually no effect on the three-dimensional flow structure behind the stage. The Rreliability of this assessment is confirmed by a comparison between the computational and the experimental data. Therefore, if the input stream has a moderate swirl, it is possible to perform a 3D simulation of the flow in a diffuser with struts, by using the domain isolated from the last turbine stage and by setting the boundary conditions at the entrance to the diffuser according to the flow calculation in the last stage of the turbine without the diffuser.