The differential cross section and total cross section of high-energy electron impact excitation can be calculated by Born approximation. The differential cross section is propotional to the so called generalized oscillator strength. The target atom or ion may be excited to infinite number of bound states and adjoint continuum states which can be treated in an unified manner by Quantum Defect Theory. Thus, we define generalized oscillator strength density (GOSD) as the generalized oscillator strength per unit of excitation energy. We have calculated the GOSD's of the lithium-like isoelectronic se-quence(Li, Be+, B++, C3+, Ne7+, Na8+, K16+) for excitation from the ground state to S, P, D and F channels. The scaling relation along isoelectronic sequence is discussed.