In the frame work of multi-channel quantum defect theory, the energy levels of three autoionization Rydberg series converging to Sc+ 3d4s(1D2) with Jπ=(3/2)-,(5/2)- are calculated from first principles by relativistic multi-channel theory at two levels of approximation, i.e., frozen core approximation and that with consideration of dipole polarization. Considering dipole polarization effect, the difference between calculated and experimental quantum defects for the 3d4s(1D2)np2D3/2 and 3d4s(1D2)nf2F5/2 series are smaller than 0.01, thus the dipole polarization effects are important for the two autoionization Rydberg series. While for 3d4s(1D2)nf2D3/2 series, the calculated data by frozen core approximation are close to those by considering dipole polarization effects, and the difference between calculated and experimental quantum defects are generally about 0.04.