Abstract: A system dynamics-based one-dimensional soil water balance model (SD-WBM) was developed to estimate water budget in root zone of winter wheat on daily basis with Vensim software. It was assumed that the 2m-soil was comprised of 10 series-wound soil reservoirs. The physical processes, such as infiltration, soil evaporation, plant root water uptake, capillary rise and water redistribution between two adjacent soil reservoirs, were calculated in the model. For validation and calibration, field experiments of winter wheat were conducted in Shijing Irrigation Scheme in Hebei Province during 2007-2009, and model-calculated soil water content of 10 soil-depth intervals from 0 to 200 cm were compared with measured water content. The results showed that mean residual ratio (MRR) and distribution root mean square ratio (DRMSR) were all less than 15% in the validation and calibration. Furthermore, assumptions in SD-WBM were proved to be reasonable, with no structural error occurring through tests under three kinds of extreme condition, such as sensitive tests of six kinds of parameters as well as comparisons with Hydrus-1d model. Simulating results of soil water budget during growing season of winter wheat indicated that precipitation and irrigation were dominant water supply with little capillary rise and large amount of percolation. And water storage changes little in the harvest day compared to that in the sowing day.