Abstract: Thermodynamic design and aerodynamic design were conducted on a radial-inflow turbine using iteration method and screening method, respectively, while an analysis was carried out on off-design performance of the turbine using three-dimensional numerical simulation. Results show that under different inlet mass flow rates, the total to total efficiency varies in different laws with the relative rotational speed. At larger inlet mass flow rates, the maximum efficiency corresponds to the lowest relative rotational speed. At the design inlet flow rate, the radial-inflow turbine could work stably at higher efficiency in a certain range of relative rotational speed. When the inlet flow rate is constant, the power output rises first and then drops with the increase of relative rotational speed; whereas, when the rotational speed is constant, the power output increases with the enhancement of inlet mass flow rate; the variance amplitude of power output reduces with rising relative rotational speed.