Avalanche ionization is a dominant damage mechanism of optical films if laser power density reaches to TW/cm2 level. In order to study avalanche ionization mechanism, it is inevitable to deal with rates of electrons absorbing and losing energy. Both of these relate to the rate of collision between electrons and phonons. So it is important to study the collision of electrons and phonons. In this paper, we discuss the effect of truncating the maximum phonon vector on collision rate, and find the relation between scattering rate and electron kinetic energy. The conclusion is consistent with that obtained from other theories and experiments. At the same time, we also modify the coupling parameter, and obtain the connection of the coupling parameter with phonon vector. After modification, the curve shape of scatter rate versus electronic energy does not change, but the overall value decreases.