Abstract: The variation of vegatation cover in a large range can change the physical properties on the surface, and influence evaporation from the surface into the atmosphere, because evaporation averaged for a long range on the whole globe should be equal to the corresponding precipitation, thus, it is possible that the variation of vegatation cover has some effects on the formation of precipitation in a certain region.In order to study the effects of the variation of vegatation cover on precipitation in a certain region and drought climate, by the improved lorenz's low-order moist spectral model, six numerical experiments whose integrational times are longer than seventy model days are designed and performed. The physical processes introduced into the model are solar radiation absorbed by the surface, exchange of sensible heat, release of latent heat, hydrological cycle, convective adjustment, frictional dissipations, land surface heat budget, orographic effects, and differences between sea and land. The experimental results show the increasing of the vegatation cover may increase the model precipitations, and shorten the durations in which the day's model precipitation is less than 1.0mm. It seems that the increasing of the degree of the vegetation cover contributes to an improvement of drought climate to a certain extent.