  I study the lattice dynamics and electron-phonon coupling in
non-centrosymmetric quasi-one-dimensional K$_2$Cr$_3$As$_3$ using density
functional theory based first principles calculations. The phonon dispersions
show stable phonons without any soft-mode behavior. They also exhibit features
that point to a strong interaction of K atoms with the lattice. I find that the
calculated Eliashberg spectral function shows a large enhancement around 50
cm$^{-1}$. The phonon modes that show large coupling involve in-plane motions
of all three species of atoms. The $\mathbf{q}$ dependent electron-phonon
coupling decreases strongly away from the $q_z = 0$ plane. The total
electron-phonon coupling is large with a value of $\lambda_{\textrm{ep}} =
3.0$, which readily explains the experimentally observed large mass
enhancement.
