Effects of competitive interaction between two mixed planting maize (Zea mays L.) cultivars on yield and water use efficiency are inevitable and the positive process needs more excavation. Two maize cultivars were mixed planting in two densities to explicit the potential of competitive interaction improving yield and water use efficiency in a semi-arid region over two growing seasons. During grain filling stage firstly, competitive interaction optimized stem to leaf ratio of two maize cultivars, and decreased root to shoot ratio at harvest under the same-high mixed planting density, great competitive intensity caused by high planting density suppressed vegetative growth of maize. Secondly, land equivalent ratio positively increased from 1.02 to 1.14, which signified the advantage of farming land use. Furthermore, positive values of total actual yield loss in the four mixed systems indicated a yield advantage. Over two years, mean yield and water use efficiency increased by 6.5 % and 11.7 % which resulted from the positive performance of two maize cultivars in the mixed systems. Thus, consequences of competitive interaction in the mixed planting systems performed as land use, maize yield and water use efficiency advantages in the dry land farming.