An experiment was conducted under continuous drying conditions in the field to examine root system growth in relation to water extraction pattern by winter wheat from 1995-1996 at Luancheng Experimental Station of Agricultural Ecosystems, Chinese Academy of Sciences which is located in the North China Plain. A model for analyzing the relationship between soil water extraction and root growth was put forward and verified. Extraction was analysed in terms of two components: (a) the time when the extraction front reaches a particular depth is defined as the moment when soil water content(θ) begins to decline exponentially with time, and (b) the decline of θ with time occurs at each depth after the extraction front arrives.Root length density declined gradually with depth, the period of fastest growth of root occurred after early head before anthesis and root length in each layer reached a maximum during flowering stage. The effect of soil water on root growth was little after anthesis, which implies that the depth and volume of soil water extraction by winter wheat mainly rely on the root length accumulation and downward penetraction during vegetative phase. The root front penetrated down to 100cm deep before jointing, thereafter the extraction and growth of root fronts descended together. Once the root front arrived at a given depth, root proliferation continued until about 40%-20% of extractable water in the layer remained. Although the maximal depth of root front penetration was up to 180cm, the ability of water uptake by root was strong and the amount of soil water available to winter wheat was much more in the lower layers, yet as the distribution amount of root system was too less that the extraction front could only arrive at 120cm, and most amount of water required by winter wheat come from 0-60cm layer.Under soil continuous drying condition, the deficiency of soil water was one of the important factors which restricted the ability of water extraction by root. The peak of extraction rate per unit root length (q) occurred near the beginning of extraction each layer. As soil dried, q declined substantially in approximate linear relationship with the fraction of extractable water (FEW) as FEW was more than 0.8.