Abstract. The paper shows the results of calculation internal head characteristics of the intermediate low-flow centrifugal compressor stages impellers. The type of stages is used at the last stages of multistage centrifugal compressors of the high and ultrahigh pressure. Inviscid quasi-three-dimensional and viscous three-dimensional calculation methods are used. Numerical models of the objects of study represent the flow part of the impeller and the blade-free diffuser with width equal to the height of the blade at the output of the impeller. For a CFD calculation, two interfaces are considered: frozen rotor and stage. It is found that the most qualitative character has a viscous calculation with the Stage interface and inviscid quasi-three-dimensional calculation.