Based upon the general FEA platform ANSYS,the numerical results of the modal analysis of a radial inflow turbine impeller are presented.The dynamical equation of impeller in the form of FEM is derived.The initial stress matrix and centripetal stiffness matrix are linearized.The eigenproblem of the dynamical equation is solved by means of Block-Lanzos method,so the 25 modes of the impeller are obtained.In addition,the simplified dynamical equation is founded upon the dynamical equation of spinning beam,in order to explain the major dynamic characteristics of the impeller,which are validated by numerical analysis.The results of the analysis indicate:because of spin softening,when approaching to critical rotation speed,the frequency of each mode is decreased,especially for the first bending mode it is more evident.Then after,when running over the critical rotation speed,the frequency of the first bending mode rises greatly.The major shapes of the impeller are coupled bending and torsion.