Abstract: A field experiment was conducted for winter wheat(Triticum aestivum L.) to explore the physiological and ecological mechanism of water utilization under different mulching treatments in semi-humid irrigated area. Daily variation and growth stage variation of gas exchange parameters of winter wheat were studied under straw mulch and ridge covered with plastic film treatments. Water use efficiency at population and yield level were analyzed. Results show that, compared with no-mulch treatment, the two mulch treatments increase the photosynthetic rate after 14∶00. Ridge covered with plastic film treatment improves the water use efficiency at leaf level(WUE_L) after 12∶00 significantly and straw mulch treatment improves WUE_L during 10∶00～14∶00 while decreases transpiration rate. The two mulch treatments increase the photosynthetic rate and WUE_L in the later growth stage but have contribute to dominance on WUE at population level and yield level. The yield of winter wheat increases significantly under the ridge covered with plastic film result from high soil water utilization. The reason of the yield reduction under straw mulch is mainly low tillering ability.