A gas-turbine-driven pump system was designed and tested. Pump systems are generally driven by an electric motor, but a gas turbine is occasionally used as the power source for high power and performance; for example, the turbopump of a liquid rocket propulsion system. For research on turbopumps, a gas generator, turbine, and pump are developed. After each component is developed, the performance should be confirmed with a link test. In the case of a turbopump, an axial turbine is applied to generate huge torque, but a radial inflow turbine was used in this research. A radial inflow turbine can be obtained easily and mass-produced. System analysis was conducted using a link test with all components at once. The turbine generated shaft power under steady operation of the gas generator, and the pump performance was measured using a stepped closing valve at the pump exit. Turbine heat loss was considered and a slip factor was applied to the impeller design to modify performance. This research shows the feasibility of developing a pump system operated by a radial inflow turbine and its application to a small turbopump for a hybrid rocket propulsion system and an air-independent system.