Based on relativistic multichannel theory, this paper calculates the energy levels of autoionization Rydberg series 4s2nf(n = 4 - 23)Jπ =(7/2)° of scandium at different levels of approximation within the framework of multichannel quantum defect theory. The present results show that the dipole polarizations play an important role. Considering the dynamical dipole polarization effects, this paper finds that the difference between calculated and experimental quantum defects for the 4s2nf(n = 4 - 23)Jπ = (7/2)° series is generally about 0.01-0.03. Furthermore, the reason that 4s216f is obscured in experimental spectra is suggested to be the interaction with the neighbouring resonance state converged to 3d2(1G4) of Sc+.