The ecosystem is important because it is the life sustaining system for human survival. Three ecosystem characteristics are: re-gional particularities, ecosystem complexity and conventional cultural particularities. This paper develops a remote sensing based dynamic model to assess grassland ecosystem service values involving multidisciplinary knowledge. The ecological value of grassland ecosystems is focused on using a remote sensing technique in the model, and setting up the framework for a dynamic assessing model. The grassland ecological services condition and value in 1985 is used as the benchmark. The dynamic model has two adjusting indicators: biomass and price index. The biomass is simulated using the CASA (Carnegie-Ames-Stanford Approach) model. The price index was obtained from statistics data published by the statistical bureau. Results show that the grassland eco-system value in Gansu Province was 28.36 billion Chinese Yuan in 1985, 140.37 billion in 1999 and 130.86 billion in 2002.