The paper presents the results of CFD calculations of a centrifugal compressor stage with a high-pressure 3D impeller and a vaneless diffuser. The stage was designed by Simonov at the LPI Problem laboratory of compressors for the design parameters: flow rate coefficient 0.080, loading factor 0,74, and the relative Mach number 0,78. Two design grids were used: 2,4 and 4,4 million cells for the sector with one blade. The entire stage was calculated with a rarer grid. Special «Stage» interface conditions were used to interface gas-dynamic parameters at the region boundary. The SST turbulence model was used in the calculations. The results of efficiency characteristics and work coefficient comparison showed the following: all three variants of the calculation overestimate the loading factor by 14,3 % in design flow rate; the calculated characteristics of the polytropic work coefficient in the staging of 360 degrees are closest to the experimental characteristics, but the absolute value is greater than 12% at a flow rate coefficient of 0.085; the maximum calculated efficiency of a stage (the circle of 360 degrees) is almost equal to the measured maximum efficiency.