The results of studies into geometric characteristics for multistage steam jet ejectors are presented. Various manufacturers’ approaches during multistage ejector design optimization are analyzed accounting for the pressure increase levels’ distribution and the nozzles’ critical diameters of the ejector stages. It was found that, for cogeneration and condensing turbines, an approach to the distribution of geometric and technological parameters over the ejector stages can vary. For cogeneration turbines, the diameters of the nozzles’ critical sections decrease with an increase of stage number, while they increase for condensing turbines. It is shown that there is a correlation in multistage ejectors between the distribution of steam flow rates between stages and the main geometric parameter of the ejector’s first stage. The test results of three- and two-stage ejectors with external coolers designed by the authors are presented. The main three-stage ejector is employed in the scheme of steam-air mixture evacuation from the turbine condenser, and the two-stage ejector with a precooler is designed to evacuate air from the scheme of the turbine heat extraction plant. The ejector of the heat extraction plant is connected to the main condensate line behind the main ejectors. Steam condensate is removed from the ejector to the hot well of the first delivery water heater. Multistage ejectors are equipped with an extended scheme for pressure measuring along the ejector’ steam-air mixture path: in the intake chamber, after the diffuser, and in the intermediate cooler. It is shown that an increase in the pressure of the steam-air mixture, which cannot be explained by the obvious diffuser effect, that is, by the pressure increase as flow decelerates, is observed in the ejectors’ coolers (between the stage diffuser and the intake chamber of the next stage). When analyzing the operating modes of multistage ejectors, the spesific feature of their self-regulation is revealed with the possibility of decreasing the steam-air mixture compression ratio in one of the stages.