It has been shown that the effect of soil drought at the initial stages of stress development does not cause significant destructive processes in the photosynthetic membranes of barley plant leaves, what has been evidenced by the absence of disturbances in the photochemical activity of photosystems 1 and 2. Moisture deficiency in the soil causes the activation of the adaptation mechanism, which consists in the redistribution of energy between PSs, which minimizes the photodestructive effect. It has been established that in the leaves of barley plants during drought, the non-photochemical quenching of chlorophyll fluorescence, which is to a greater extent its regulated component, is significantly reduced. This is potentially dangerous, since the chloroplasts of such plants will be vulnerable to photooxidative stress under prolonged stress. The suppression of the controlled energy dissipation in the photosynthetic membrane during drought may be the limiting factor determining the resistance of barley plants to such stress.