Abstract: To continue the experimental test on a 350 kW organic Rankine cycle (ORC) unit after its blade fractured under full load condition, the nozzle and impeller of the radial turbine were specially optimized without any change to the volute, including adjusting the number and improving the profile of the nozzles and blades, and optimizing the flow path of the impeller, etc. The unsteady flow field in the radial turbine was simulated before and after optimization, while transient dynamics of the optimized impeller were analyzed at rated speed and load. Results show that in comparison with the old impeller, the new one is subject to sharply reduced excitation force of gas flow, with greatly lowered average stress and relatively small dynamic stress, which is safe enough in both static and dynamic status.