Abstract: As a case study of Xi'an City, the virtual water and the total amount of virtual water were calculated using the meteorological data and data from statistical yearbook of Xi'an from 1980 to 2014. By the means of EMD, the Empirical Mode Decomposition method, the influencing factors of total amount of virtual water were discussed and studied atspatio-temporal multiscale. Results show as follows:(1)The total amount of virtual water in Xi'an showedan increasing trend expect for the year of 1982, 1992 and 2014. There werea 3-year-cycle fluctuation and a 10-year-cycle fluctuation in the gross amount of virtual water, and the 10-year-cycle wasthe main fluctuation.(2)At the spatial-temporal multiscale, the 3-year quasi-cycle fluctuation of total amount of virtual water was affected by the grain yield and crop virtual water. The 10-year cycle fluctuation of total amount of virtual water was mainly affected by the crop virtual water before 1990 and the grain yield and the crop virtual water after 1990.(3)The study of three zones by EMD reveals that in short period, the three zones of Xi'an City wereall the control areas of the 3-yearquasi-cycle fluctuation of Xi'an city's total amount of virtual water; from high to low, the degree of impact ranked as: suburbs county, outer suburb district and the city six districts; in the long period, outer suburb district and suburbs county werethe major control areas of 10-year-cycle fluctuation of Xi'an city's total amount of virtual water, and outer suburb district was thefirst control zone. The paper provides a better understanding of the water resource consumed by grain production in Xi'an; it also facilitates a more scientific regulation of grain production; furthermore, it provides a reference for similar cities thatare short in water resource to mitigate the pressure on water resource and develop a strategy for grain production.

Key words: virtual water, empirical mode decomposition method, spatial-temporal multiscale, Xi'an City