The ecosystem is important because it is the life sustaining system for human survival. Three ecosystem characteristics are: regional particularities, ecosystem complexity and conventional cultural particularities. The researchers 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 ecosystem value in Gansu Province was 28.36 billion Chinese Yuan in 1985, 140.37 billion in 1999 and 130.86 billion in 2002.