We report a theoretical study of vibronic effects on the 1t1 → 3s Rydberg excitation in CF4 induced by electron impact. The generalized oscillator strength for the excitation has been calculated using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. In the calculation vibronic effects have been taken into account by evaluating the electronic transition moment along the individual normal coordinates. The present calculation successfully reproduces our recent experimental result N. Watanabe, D. Suzuki, and M. Takahashi, J. Chem. Phys. 134, 064307 (2011)10.1063/1.3549135 over the full momentum transfer region studied. By examining contributions from individual normal modes, the asymmetric stretching mode is found to play a leading role in the 1t1 → 3s transition at small momentum transfer.