The study presents the results of CFD calculations of for a flow part of a two-stage 16 MW pipeline compressor. The calculated characteristics of the pressure ratio, efficiency and work coefficient are compared with the characteristics measured at the manufacturer's air test rig. The calculations are performed in two ways, without and with modeling the flow in the "impeller – stator" gaps. In the first case, friction losses of the outer surfaces of the impeller and leakage in labyrinth seals are not taken into account. The «STAGE» interface connects parameters of the flow at the impeller exit and vaneless diffuser inlet. This approach excludes the mixing of high-and low-energy flow zones in the diffusers from the calculation. The calculated characteristics are close in form to the experimental ones, but they are shifted to the area of higher flow rates, differ in efficiency and pressure ratios within the limits unacceptable for using CFD calculations instead of tests.