The middle and upper atmosphere can be affected by solar activity in a number of ways, i.e., through a modification of the temperature and wind and/or through the generation and modulation of atmospheric and hydrodynamic waves. The present paper is devoted to study of Atmospheric Gravity Waves (AGW) propagation under different temperature and wind conditions as one of such mechanisms. A set of runs with a linearized numerical model of the plane monochromatic AGW propagation using one of the known empirical spectra and the background conditions (wind and temperature profiles) for different levels of solar activity is performed. The results obtained show that efficiency of the energy and momentum transfer from the lower into the upper atmosphere by the AGW and the mean flow acceleration caused by the AGW dissipation due to thermal conduction and viscosity strongly depends on the level of solar activity. It also has been found that the main effects of the modulation of AGW propagation by the solar activity are observed in the thermosphere. The conclusion that energy and momentum transfer from the lower into the upper atmosphere by AGW and probably other waves is very sensitive to the variability of solar activity.