On the basis of overview of the study area, by analyzing the dynamic change of farmland in Ninglang County, we can find that the farmland area in this county tended to decrease from 1996 to 2008. According to the investigation data concerning land change provided by Bureau of Land and Resources in Ninglang County and socio-economic data provided by Bureau of Statistics in Ninglang County, we select 11 indices, such as total population, GDP, total output value of county and so on, coupled with SPSS statistical method, we adopt principal component analysis method to analyze driving force factors of farmland use change in the high and cold areas in Northwest Yunnan. The results show that the two factors of economic development and population growth are the dominant driving factors impacting farmland use change, and the policy factors, such as “returning farmland to forests”, are also the important driving factors impacting Ninglang County.