Abstract: Field experiments showed that the straw mulching could change crop water consumption. Soil evaporation in mulched field was reduced in early stages of winter wheat and plant transpiration was enhanced at late stages. It was favorable for dry matter accumulation and change water consumption from physical process into biological process. The yield and water use efficiency of winter wheat in mulched field were raised into a higher level. The beneficial results of straw mulching were different at different soil water contents and different mulching times. The highest yield and water use efficiency were obtained from the field where soil water content was 55%～70% of field capacity and mulching date was on December 20, when winter wheat stopped growing in winter.