The estimation method of the ecosystem service value per unit area proposed by Costanza et al. is a crude approximation without consideration of the spatial heterogeneity within the same biome. It is based on the values of the structure and functions of the ecosystem and hence named as static evaluation here. When it is used for optimal allocation of water and land resources in a basin to obtain maximal integrated social, economic and eco-environmental benefits, such method can’t reflect the scarcity of ecological resources and the willingness-to-pay of individuals for ecosystem services, which will appear with the social and economic development and the depletion of ecological resources. Therefore this method is difficult to be applied. 
Here the concept of a dynamic evaluation of the ecosystem service values is proposed. It is a currency value based on the current willingness-to-pay of individuals for ecosystem services. Referring to the method of Costanza et al., a modification coefficient for the ecosystem service value per unit area is proposed according to the cover degrees of biomes combined with expert consultation. Based on the developmental coefficient and scarcity of ecological resources, a dynamic evaluation method is proposed. The Shiyanghe River Basin in the Hexi Corridor of Gansu Province is selected as the study area. The annual static value of the ecosystem services in the Shiyanghe River Basin is estimated as 0.417 billion $, equal to 0.3657 times of the local GDP in 2000, and showing a descending trend from the upper reaches to the lower reaches. The annual dynamic value is 0.235 billion $, more in the lower and upper reaches than in the middle reaches. This study shows that the dynamic evaluation method is useful for the optimal allocation of the natural resources.