Studies on the effect of different levels root cutting on the photosynthesis rate, stomata conductance, aboveground biomass, grain yield, and water use efficiency of maize showed that moderate root cutting could improve its photosynthesis ability, and increase its aboveground biomass and WUE. On the contrary, when the roots were cut severely, the photosynthesis ability was weakened, and the biomass was decreased. Moderate root cutting could increase maize grain yield, but the effect was not significant.