Abstract: This paper aims at applying the principles of water balance and the semi-fixed dunes for the establishment of the product-protective systems in Maowusu Sandland (Zhang Xinshi, 1994; 1996)to the practices of afforestation and control of desertification. As water serves as alimiting factor for the shrubs ecosystems in China’s Maowusu Sandland,one of the shrubs ‘kingdoms’ in the temperate arid zones of the world, it is very important to estimate the appropriate planting densities with the aid of the principles and methodologies of water balance for the rational management and sustainable development for the area’s vegetation. In this, evapo-transpiration (ET) is the most difficult to be determined accurately. This paper proposes a method for the estimation of seasonal transpiration water loss based on field measured data of transpiration rate ,considering the typical pattern of change of above-ground green biomass during the typical growing seasons from mid-April to mid-October. The evaporation from sand surface during the growing seasons is estimated by using a semi-empirical model and taking the monthly mean temperatures at sand surface as the input. Finally, the appropriate planting densities for the major shrubs are discussed as constrained by the water balance equation. According to the results obtained, the evapo-transpiration of the shrubs ecosystems of Maowusu Sandland comes mainly from plants rather than the soil. As a result, the appropriate planting densities for the dominant shrubs ought to be controlled at such a level that the dunes are semi-fixed by the plants, with the exception of Sabina vulgaris stands having a high density owing to its powerful capability of transpiration control.