An experiment about the effect of soil evaporation prevention agent called Guilspare was carried out using subsurface drip irrigation on soybean farmland. The results were summarized as follows:under the condition of 1%，2%spraying concentration and 50 0 0，100 0 0 of field water capacity，average soil water contents attained 14. 07%，7. 46%;22. 48 0 0，12. 89%improvement against the contrasts respectively

so better water retention effect was observed under 2%spraying concentration than that under 1%concentration.Obvious soybean growth improvements were observed both under different concentrations and irrigation con- tent:for the soybean yield

its increasing effects were 6. 08%，9. 39%;11. 49%，16. 02%under 1%，200 spraying concentrations and 50%，100%.There was more remarkable yield increase under 2%spraying concentration than that of 1%.At last，under condition of spraying concentration 2%and 50%field capacity irrigation，WUEI reached its maximum value 1. 06 kg/m'，the integrative effects of productivity increasing and water saving were mostly obvious.