Abstract: Using straw to cover wheat field is an effective measure to reduce uneffective evaporation from interplant and increase the untilization efficiency of water resources.Results from three years′experiments showed that water consumption coefficient was reduced by 8.1 to 23.2% and evaporation from soil surface was reduced by 26.3% by straw mulch.The total water-saving amounted to 270m³/hm².The mechanism of straw mulch in water-saving is that straw mulch can adjust soil temperature,conserve soil moisture,inhibit weed growth and improve the utilizaton efficiency of soil water.