Movement of water in the ”soil-plant” system is carried out by the inflow of moisture from the soil through the roots into the plant and the expenditure of moisture by the plants on evaporation into the atmosphere. The speed of motion is determined by the intensity of transpiration, which depends on the intensity of atmospheric conditions. Investigations of Averyanova S.F., Golovanova A.I., Nikolyskovo Yu.N. (1974) [1] found that the distribution of moisture absorption over the depth of the aeration zone depends on the moisture content of the soil and as the humidity increases from the wilting moisture to its maximum value, the amount of absorption increases. Since the proportion of water that takes part in the construction of organic matter is very small in comparison with transpiration, the water costs of plants are determined by the intensity of transpiration, which is an indicator of the moisture content of plant tissues. In many cases, the function of moisture selection is an integral part of complex mathematical models and only in their framework is`t manifested well [3, 10, 13]. The analysis has shown the importance and necessity of determining the functions of moisture selection by the root system of the grown crops from the dried soil profile, since taking into account the spatial features of the processes of moisture absorption by the plant roots. Makes it possible to predict the moisture regime of the root layer of the soil and conduct drainage and moisturizing measures in the reclaimed lands of the humid zone more reasonably and qualitatively. Spiet D.A., (1982) as well as Gardner W.R., Taylor H.M., proposes to find the value of transpiration by assuming that the flow from the soil to the root systems is of a radial nature [4, 11, 15]. Therefore, when choosing the structure of models of moisture absorption by cultivated crops along the depth of the root-layer of soil, first of all, sufficient simplicity and reliability of obtaining experimental information for the purpose of using these models in production conditions were taken into account.