Development of design procedure of expander-compressor units (ECU) of cryogenic air separation plants (ASP) is actual. Distinctive features of designing of the one-stage centrifugal compressor step included in ECU are marked. Formation of system of the initial data for calculation of compressor step (CS) of ECU is considered. Results of the comparative analysis of influence of compressor and expander steps efficiency on similar parameter of ECU are resulted. Recommendations concerning creation of design procedure of CS are given.