Abstract: The experiment of controlled rootdivided alternative irrigation (CRAI)in maize showed that controlled 1/2 root region alternative irrigation in 55 %～65　% of field water capacity is able to save 34.4 %～36.8 % of water use, and the biomass only decrease 6 %～12 %． The efficiency of water use and the rootshoot ratio increase obviously. The transpiration efficiency increases because the photosynthesis is not changed　but the stomatal resistance increases and the transpiration rate decreases. The water use efficiency of 1/2 rootdivided alternative irrigation is higher than that of 1/2 rootdivided fixed irrigation. The weight of dry root and rootshoot ratio increase and the root distributes evenly by alternative irrigation, but the 1/2 root divided fixed irrigation has no this effect. Controlled RootsDivided Alternative Irrigation is a practicable technology of water saving.