In this work a new method of the rationalization of the soil moisture regimes is presented. For that purpose we have elaborated a new model of planification and maintenance of rationalized/optimized soil moisture regimes based on aridity index. The algorithms for the determination and the maintenance of irrigation regime that we have elaborated, can be used either while planning the systems of irrigation, or further, while their exploitation when there appears a necessity of saving water for irrigation. This method offers the possibility of planification and maintenance of a hydrothermal regime allocated for irrigated enclosure. The algorithms for determination and maintenance of irrigation regime that we have elaborated, can be used either while ecological optimization of hydrothermal regime of irrigated surface, or, while economic optimization of irrigation systems expenses. The results of our investigation were verified in conditions of lysimeters installed in the State Hydro meteorological Service area. The components of radiation balance used in the elaboration were taken from the State Hydro meteorological Service.