  Nuclear excitation cross section of $^{229}$Th from the ground state to the
low-lying isomeric state via inelastic electron scattering is calculated, on
the level of Dirac distorted wave Born approximation. With electron energies
below 100 eV, inelastic scattering is very efficient in the isomeric
excitation, yielding excitation cross sections on the order of 10$^{-27}$ to
10$^{-26}$ cm$^2$. Systematic analyses are presented on elements affecting the
excitation cross section, including the ion-core potential, the relativistic
effect, the knowledge of the reduced nuclear transition probabilities, etc.
