To understand the mechanization of the efficient water utilization on summer maize, field experiments involving straw mulching with 0, 0.6 kg/m(2)(N and M, respectively) and plant density with 10.0, 7.5, 5.5 (1, 2 and 3, respectively)plants per m(2) were conducted. The effect of straw mul-ching and plant density on soil moisture content under different layer, grain yield and yield components was investigated, to discuss the potential of grain yield and WUE improvement by the optimized combination of straw mulching and plant density. The results show that the yield and WUE of M2 treatment are 1255.44 g/m(2) and 3.93 kg/m(3), respectively, which are higher than other treatments. Evapotranspiration has no significant difference among different straw mulching treatments in the whole summer maize growing season. Straw mulching improves the 0-30 cm soil moisture content in medium growing stage under low density treatment, ear number, 1000-kernel weight, grain, WUE by 8.67%, 3.73%, 8.04%, 16.88%, 21.94%, respectivel