Field experiments were conducted to study the effects of supplemental drip irrigation on maize growth (Zea mays, L.), yield and water use efficiency under plastic mulch at the Loess Plateau Changwu Experimental Station in Shaanxi Province of Northwest China in 2010 and 2011. The field experiment was performed in an randomized block design, which consisted of a full irrigation check treatment at four different growth periods (seedling stage, jointing stage, filling stage and mature period) under four levels of supplemental irrigation which were based on different coefficients of a Class A pan (Kpc) (F: 0.4, S: 0.6, E: 0.8) treatments and each time for irrigation frequencies ranging from 2 to 7 days under a drip system. The highest evapotranspiration of the whole maize growing season occurred under full irrigation. Maize mulching (M) during the growing season has little effect on leaf area. Supplemental irrigation during the jointing stage addresses the critical period for the growth of maize height. Plastic mulch has obviously leaded to increased maize yields. Thus, the most effective factor for increasing maize grain yields corresponded to supplemental irrigation during the jointing and filling stages. More irrigation results in a greater the yield, but irrigation water use efficiency did not increase. Supplemental irrigation ranged from 40 to 135 mm, and the results indicated that every 1 mm of supplemental irrigation water could increase grain yields by average 45 kg/ha of all treatments. Despite the reduction of biomass and grain yield in the treatment 6 (MFSSS), a supplemental irrigation quantity of 88 mm was optimal for 2010 and 2011, because it resulted in higher maize production and irrigation water use efficiency in the Loess Plateau of Northwest China.