This dissertation considers problems appearing in different applications of high-speed technology from the viewpoint of the rotor structure. In this study high-speed technology refers to a system in which the electric machine (motor, generator) and the unit to be driven (turbine, compressor, blower) are directly coupled to each other without a gear box and the speed of this common shaft is significantly higher than the synchronous speed of a two pole electric machine connected to a 50 or 60 Hz network. High power density and high mechanical load is typical for the rotor of a high-speed machine. Therefore, for example, the cooling of the electric machine is challenging because of the relatively high iron losses and small heat transfer areas. The objectives of this study can be divided into three parts:  Analysis of the mechanical structure of high-speed turbomachine rotor, to decrease heat sources and to increase the cooling of critical points. This involves the decreasing of electrical losses and the concentration of these losses in areas which are favourable for the cooling  Analysis of the mechanical structure of high-speed turbomachine rotor to raise the first bending critical speed of the rotor  Analysis of the mechanical structure of high-speed turbomachine rotor, from the viewpoint of the structural strength. This involves different interference fits and their stability at high speeds, including their stiffening effect and heat transfer properties. The scientific contribution of this work is particularly the analysis of the mechanical structure of the combined electric machine and turbo machine rotor, taking simultaneously into account all the three viewpoints mentioned above: the cooling (including the hot spots), the reduction of electrical losses and the analysis of their distribution, the elevation of the rigidity of the rotor, the proper control of stress levels and mechanical stability of the structure, and the analysis of thermal resistance in the interference fits.