Abstract: Field experiments were carried out to verify the optimum uncovering plastic film period and nitrogen rate for higher yield, water use efficiency and better physiology, growth condition of maize in mulched fields in the Guanzhong Region, Shaanxi Province and to provide basis for the development of rational cultivation measures. Under field condition, three uncovering plastic film periods (uncovering plastic film at the jointingtasselling stage, uncovering plastic film at the tasselling stage and mulching plastic film) and three nitrogen rates (N 0, 120 and 240 kg/ha) were applied to study the interaction between uncovering plastic film period and nitrogen rate on physiology, growth, yield and water use efficiency of film mulching summer maize. The results show that uncovering plastic film period and nitrogen rate have significant effects on physiology, growth, yield and water use efficiency of summer maize, and the interactive effect between them is not significant. Through improving the gas and heat conditions around the roots, and increasing the root activity, the uncovering plastic film at the tasselling stage increases the plant height, leaf area, and dry mass accumulation and leaf photosynthetic rate, decreases the leaf MDA content, and has better ear characters, yield and water use efficiency in comparison with the mulching plastic film treatment under the three nitrogen rates. However, there are no significant differences between the uncovering plastic film at the jointingtasselling stage and the mulching plastic film treatments. With the same uncovering plastic film period, applying nitrogen fertilizer amounts of NL (N 120 kg/ha) or NH (N 240 kg/ha) are better than that of the NZ (N 0) treatment in the physiology, growth, yield and water use efficiency of summer maize, however, there are no significant differences between the NH and NL treatments. As the increasing of nitrogen rates, the leaf photosynthetic rate, yield and water use efficiency are decreased, while the leaf MDA content is increased. In this study, taking yield, water and nitrogen use efficiencies and environment effect into consideration, the appropriate uncovering plastic film period and nitrogen rate of summer maize in mulched fields in the Guanzhong Region are uncovering plastic film at the tasselling stage and N 120 kg/ha respectively, the yield and water use efficiency of which are 11362 kg/ha and 34 kg/(hamm).