Abstract: Using cucumber as the test plants and sand as substrate to study the effect of different water retaining agents(WRA) and their application rates on the growth and water use efficiency of the plant, the porosity, the water retention and properties of the substrate. The results showed that, for both copolymer of polyacrylamide and polyacrylate and polyacrylate , the total porosity, wet weight of the seeding and water use efficiency(WUE) were significantly increased along with the increase of WAR application rates, while the big and small pore space ratio, aeration capacity, amount of water evaporation per day, cumulated amount of water loss reduced. Higher rates of application, however, with a strong water retaining capacity and effect on prolonging the wilting time of the seeding, did not benefit the seeding because of the decrease of aeration pore space. Considering the whole results, copolymer of polyacrylamide and polyacrylate had better effect than polyacrylate.