Abstract: Experiments were carried out to study the effects of different fertilization levels on water use efficiency (WUE) of winter wheat (Triticum aestivum cv. Shaanhe No.6) grown in the field under dryland conditions at Luojiawa, Chengcheng, Shaanxi in 1987—1988 to explore the physiological mechanism of“regulating water using fertilizer”. The results showed that: (1)Fertilization on dryland raised not only soil water content, but also soil water potential, thus increased water use. (2) Fertilization on dryland increased leaf area of winter wheat, delayed leaf senescence, thus reduced soil evaporation, increased the potential of water-use by transpiration and the potential of photosynthesis. However, the net assimilation rate was apparantly not significantly affected. (3) Fertilization increased total water use (ET) and water-use by transpiration (T) of winter wheat under dryland conditions, increased above ground biomass yield and grain yield, so that WUE of winter wheat was improved. (4) Fertilization has the effect of regulation to winter wheat underrdryland conditions, making the plants more efficient in water economy, and hence more adaptable to drought enviroment.