Qingdao is one of the cities in North China, running short of water supply. So it is very important to preserve and save water resources for Qingdao’s sustainable development. In this paper, on the basis of a large number of field experiments and long-term stationary observations conducted in farmlands in the Dagu River Basin in Qingdao, a series of basic information, such as soil moisture, groundwater table depth, soil physicochemical properties, precipitation, irrigation, meteorology and some others were acquired for analysis and computation with the soil water balance equation coupled with the Hydrus-1d software to explore relationship between farmland soil water and groundwater in areas with shallow groundwater table, and further to determine quantity of the soil water resources in this region. Results show that soil moisture regime responds quickly to precipitation and depth of groundwater table; soil water and groundwater supplements each other mutually; and the transformation varies in characteristic with the season. During the corn growing season, soil water and groundwater exchanges frequently, as a result, soil water leaching and drastic fluctuation of groundwater table is likely to occur. During this period, soil water supplements groundwater with 228.0 mm of water and the latter does the former with 287.5mm, while during the wheat growing season, as there is no irrigation done, the relationship of mutual supplementation almost becomes that of one-way supplementation, that is, from groundwater to soil water, quite stable in rate, compared to the corn growing season, soil water supplies groundwater with 70.09 mm and the latter does the former with 266.9 mm. Through calculation, the soil water resource in the study area was worked out to be 4.395 million cubic meters and plays an important role in guaranteeing crops growth. It is essential to formulate a reasonable irrigation scheme so as to make the best use of the soil water resources, and to achieve the goal of water saving agriculture.