Abstract: The evapo-transpiration dynamics and soil water utilization characteristics of Viola poapratensis and Poa pratensisl populations were studied under long-term soil drought stress from July to September in 2006.The results showed：（1）the average survival days of Poa pratensisl and Viola poapratensis populations were 46d and 41d,respectively,under evapo-transpiration,in contrast,the average survival days were 23d and 24d,respectively,in nomal conditions.（2）The evapotranspiration per day of Poa pratensisl population were higher than that of Viola poapratensis when soil moisture were beyond 75% and 80%.But when soil water fluctuated from 30% to 80%,the evapo-transpiration per day of Viola poapratensis were higher than Poa pratensisl population.（3） Wilting coefficient of Viola poapratensis was lower than that of Poa pratensisl population. （4）The soil moisture utilization rate of Viola poapratensis and Poa pratensisl population were 78.03% and 70.00%,respectively,under long-term soil drought stress The soil water utilization rate of Viola poapratensis were higher than that of Poa pratensisl population.among 0-5cm,5-10cm and 10- 15cm soil layers.