By using the energies of the Is2nd(n=3-5) and Is2nf(n=4-6) states for a lithium atom, calculated with the full core plus correlation method, quantum defect functions are botained which vary smoothly with energy based on quantum defect theory.Then these functions are separately used to construct a system equation to calculate the energies and quantum defects of the Is2nd and Is2nf(n=7-11) states for the lithium atom. Separations betweent the centres of gravity of the nd and nf levels(n=7-11) are also predicted and compared with the experimental and theoretical data available in the literature.