Irrigation plays an important role in solving the food security problem. Hence, subsurface drip irrigation (SDI) becomes more and more widely used. Its expansion requires studies to determine the parameters of wetted zones for various conditions. We propose to study the process of wetted zones formation in soil using mathematical modeling by solving the initial-boundary value problem for moisture transport equation in vadose zone of soil. Using the proposed approach, the determination of wetted zones under SDI was performed for Ukrainian soils of different texture. Based on the results of mathematical modeling, the main parameters of wetted zones were determined. Empirical dependencies of wetted zone parameters on the structural parameters of SDI systems and pre-irrigation threshold were also established. With a decrease in the pre-irrigation threshold, all wetted zone parameters increased and the process of zone's formation for sands, sandy loams, and light loams can be described by linear dependencies, while for medium loams, heavy loams, and clays they have a polynomial form.