The experiments of different mulching methods were conducted at the agrometeorological experimental base of Chinese Meteorology Administration. The objective was to investigate the effects of different mulching methods on the diurnal variation of photosynthetic rate and water use efficiency (WUE) for summer maize, and to investigate the physiological and ecological mechanism. The experimental results are as follow: The most notable difference of diurnal variation of photosynthesis rate was observed at the morning, The Pn of the mulch is higher than that of CK. The leaf WUE was more high than CK, especially, in afternoon. It shows that mulch improve the leaf WUE, and ultimately improve yield WUE.