Abstract: Based on the simulation tests, effects of water-retaining-agents and its concentrations on moisture evaporation in the soil were studied in lab. The results showed that moisture evaporation treated by different species of waterretaining-agents increased firstly, and then declined with water stress degree time extended. The moisture-preserved capacity of soil, treated by water-retaining-agents, became stronger than that without water-retaining-agents. Among all water-retaining-agents, the effect of " Kehan 98" was the best in reducing the evaporation during the whole process. Among 4 water-retaining-agents, the effect of treatment of 0. 5%and 0. 3%were better than the others. On the contrary, water-retaining-agents in high concentration was against moisture-preserved capacity in soil. The results showed that the water-retaining-agents could improve strong the moisture-preserved capacity in soil effectively. Only right concentration could make the water-retaining-agents work adequately.