By fitting the empirical pseudopotential band structure data using piecewise pol ynomials, an analytical band model of ZnS is presented for thin-film electrolumi nescent devices. The density of states and scattering rates are calculated using the above model. As compared with the results from the full band model, we have shown that our model, which takes less time, has the same precision as that obt ained from the full band model. Using Monte Carlo method, we simulated the field -dependent electron occupation functions of 1st and 2nd bands, electron energy d istribution functions under four-electron fields and the dependence of electron energy on time with or without impact ionization. This shows that the inter-vall ey scattering, inter-band scattering and impact ionization are important for tra nsporting electrons among valleys. Another important result is that the effect o f impact ionization on current multiplication and electron energy distribution i s also discussed.