Turbine is one of the key components in organic Rankine cycle, and its aerodynamic performance and geometric dimension affect the performance of the system directly. This paper presents the one-dimensional design and three-dimensional CFD analysis for an ORC radial-inflow turbine based on the parameter optimization of the system under low grade heat source conditions. Real Gas Property (RGP) file is encoded by using the NIST REFPROP database to guarantee the prediction accuracy of the working fluid properties. The results comparison between the one-dimensional design and the three-dimensional CFD simulation is carried out. What's more, the addition of splitter blade to the rotor passage is considered to optimize the ORC radial-inflow turbine. It is concluded that the three-dimension CFD results are in good agreement with the one-dimensional analysis. And the addition of splitter blade is benefit to improve the performance of the ORC radial-inflow turbine.