In the frame work of multi-channel quantum defect theory, the energy levels of Rydberg series of ss 2 S 1/2 , np 2 P 1/2 , np 2 P 3/2 , nd 2 D 3/2 , nd 2 D 5/2 , nf 2 F 5/2 and nf 2 F 7/2 of alkali-metal atom are calculated by the relativistic multi-channel theory, in five different approximations, i.e., frozen core approximation, with consideration of ∆l = −1 dipole polarization effect, ∆l = +1 dipole polarization effect, ∆l = ±1 dipole polarization effect, stretch effect, and both dipole

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... ization effects and stretch effect, respectively. The present calculations show that electron correlation effect plays an important role in the energy level of Rydberg series. In summary, dipole polarization effect is more important than the stretch effect, and the ∆l = +1 dipole polarization effect is more important than ∆l = −1 dipole polarization effect. However, stretch effect is more important for energy levels of both Rydberg series ns 2 S 1/2 ,(nd 2 D 3/2 ,nd 2 D 5/2 ) of Na, and Rydberg series (np 2 P 1/2 ,np 2 P 3/2 ) of Li.