We considered the key ecological function area Xishui County of Guizhou Province as the study area and discussed the use of Gross Ecosystem Product (GEP) as a method to assess ecological conservation effects in key ecological function areas. By assessing the GEP of Xishui County in 2000 and 2010, we analysed the current and temporal differentiation characteristics of ecosystem service values to obtain the ecological conservation effect. The results indicated that the GEP of Xishui County was 22.335 billion Yuan in 2010, which is about 4 times the county's gross domestic product (GDP) of the same year; from 2000 to 2010, the GEP increased by 3.787 billion Yuan, with a growth rate of 20.42%. As a whole, the effect of ecological conservation effect in Xishui County is quite remarkable. This can be mainly expressed through increasing values of the amount of ecosystem products and services supplied by Xishui County during the study period (2000-2010). At the same time, the areas of the forestland and grassland of Xishui County have gradually increased. We also explored the effects of land use changes on ecosystem service values, to reveal the causes of changes in these values, which can effectively protect the ecosystems in Xishui County and achieve ecological and economic sustainable development for the region.