The imbalance of land-surface water budget was discovered in past studies,but there have been few further investigations on the relevant causes.To probe into the problem,annual variations of precipitation and land-surface evapotranspiration were analyzed by using the historical observation data from a comprehensive land-surface observation base of LOPEX (Loess Plateau Experiment).A remarkable imbalance in the land-surface water budget was found,and the total annual imbalance reached 20.6%.Then,the impact factors related to additional water budget components and observational methods were studied.The total annual imbalance could be reduced to 3.8% by using a combination of compensated land-surface water budget components and the surface evapotranspiration values obtained from the large-scale weighing lysimeter rather than from the eddy correlation method. The imbalance of land-surface water budget was discovered in past studies, but there have been been further few investigations on the relevant causes. To probe into the problem, annual variations of precipitation and land-surface evapotranspiration were analyzed by using the historical observation data from a comprehensive land-surface observation base of LOPEX (Loess Plateau Experiment). A remarkable imbalance in the land-surface water budget was found, and the total annual imbalance reached 20.6%. Then, the impact factors related to additional water budget components and observational methods were studied. The total annual imbalance could be reduced to 3.8% by using a combination of compensated land-surface water budget components and the surface evapotranspiration values ​​obtained from the large-scale weighing lysimeter rather than from the eddy correlation method.