The CO 2 flux concentration gradient and microclimate characteristics of a summer corn community were measured with an infrared CO 2 analysis system and a Bowen ratio device. The instantaneous CO 2 flux density and the water use efficiency of the corn canopy were calculated. The result showed that the CO 2 flux and CO 2 concentration gradient as well as the water use efficiency of the summer corn community had distinct daily and seasonal change patterns. The daily change of the water use efficiency was described in a ‘L’type curve with a peak value around 8 a.m. in the morning. Before grain filling, the water use efficiency increased as the corn grew, while it decreased after grain filling because of the decrease of photosynthetic ability of the corn community and the increase of respiration consumption. The water use efficiency was affected by the factors such as global radiation and CO 2 concentration and air saturation deficit etc. Therefore, in agricultural practice, the water use efficiency of the corn community could be raised by means of straw cover and sprinkling irrigation to reduce drive potential of transpiration.