In recent decades, the water cycle process in the Loess Plateau has changed dramatically under the influence of human activities and climate change. To better understand the changes in the water cycle structure, based on precipitation, evapotranspiration, runoff, soil water storage, and social and economic water use from 1982 to 2010, this study explored the water balance of the Loess Plateau by using the Mann-Kendall trend test and linear regression analysis method. More importantly, we detailed the composition of the water cycle 12 kinds of hydrological variables (respectively precipitation, changes in soil water storage, runoff, canopy interception, soil evaporation, transpiration, irrigation, mining, manufacturing, livestock, power generation, and domestic water use) and analyzed the changing trend of each component of the water cycle and the evolution of its structure. Unfortunately, because the gridded social and economic water use data (1982-2010) had imposed a relatively large time limit on the research, this study paid more attention to explore the changes in hydrological variables and the evolution of the water cycle structure in the Loess Plateau during the last 29 years (1982-2010). The results showed that in the natural system, evapotranspiration significantly increased at a rate of 1.97 mm/a(P<0.01). By contrast, runoff, precipitation, and soil water storage significantly decreased at a rate of 1.01 mm/a(P<0.01), 0.77 mm/a, and 0.46 mm/a, respectively. In the social system, the social and economic water use increased at a rate of 0.50 mm/a, which was mainly due to the increase of domestic (0.22 mm/a), manufacturing (0.23 mm/a), power generation (0.30 mm/a), and mining (0.01 mm/a). Moreover, irrigation and livestock water use significantly decreased at a rate of 0.25 mm/a(P<0.05) and 0.01 mm/a(P<0.01), respectively. For the water cycle structure, the multi-year average evapotranspiration and the average social and economic water use accounted for 80.95% and 15.27% of the water cycle, respectively, and gradually increased at a rate of 0.16% and 0.06% per year. The annual average runoff and soil water storage changes accounted for the average ratio of 4.00% and -0.24% in the water cycle, and gradually decreased at a rate of 0.24% (P<0.01) and 0.02% per year. With the rapid development of the social economy and the growth of the population, the competition between the supply and demand of regional water resources would be further intensified more severely. Our study has obviously important reference significance for the scientific regulation and sustainable use of water resources in the Loess Plateau.