In the present study, the effects of the stagger angles on the aerodynamic performances in the vaned centrifugal compressor has been investigated by CFD methods. The diffuser vane angles were varied in the range of ${pm}10$ deg. from the initial-design points. The commercial Navier-Stokes solver, ANSYS-CFX were applied to solve the impeller-diffuser flowfields. Through the numerical results, the desirable setting angles were proposed to fit the best performance to the variation of the operating conditions.