The cylindrical film seal, with prominent advantages of non-contact, little wear, long durability and high stability, is suitable for high-speed turbomachinery theoretically. To improve the leakage problem and design seals with significant performance for supercritical carbon dioxide (SCO2) turbomachinery, this paper establishes a spiral-grooved cylindrical film seal structure and aims to numerically investigate the effects of structural and operating parameters. The hydrodynamic characteristics are obtained by the computational fluid dynamics method. It indicates that with the increase of eccentricity, the leakage, floating force, friction torque and Nu all ascend. When the film thickens, the leakage increases while the floating force and friction torque decrease, and there is a transition from heat dissipation to absorption. The rotating speed and inlet pressure have a significant influence on the sealing performance under different working conditions. The leakage, floating force, friction torque and Nu all rise up with the increase of inlet pressure. The leakage and Nu decrease while the floating force and friction torque increase with the escalation of rotating speed. In addition, great results are obtained by arranging cylindrical film seal on the impeller back of a SCO2 radial-inflow turbine. Its power and efficiency are only slightly reduced by 0.58% and 0.41% respectively compared with the configuration without considering leakage, which suggests the potential applicability of cylindrical film seal to SCO2 turbomachinery.