The understanding of population variation and inferring of population development is an important basement for planning decision of social and economic development. This study investigated the characteristic of population variation in Yilan County on basis of population database recently, and predicted the population growth in the future. Traditional prediction method will often face problems of model complex, hypotheses of model not accordance to realistic environment and low precision, etc. while during few data, complicated factors and uncertain conditions. Grey prediction method can effectively improve these problems. This study first calculated the population development in Yilan County by grey prediction method, then compare traditional regression method focused on forecastability. After the investigation and analysis of this study, grey prediction method in population prediction is more effective and accurate then traditional regression method on forecastability. The ratio of advanced age people (more then 65 years old) in Yilan County is 12.6%, which is in accord with the definition of a society of advanced age by World Health Organization of United Nations. On account of the central location in Yilan County, the urbanization of Yilan City and Luodong Township are highest then other districts. So the population growth of two districts is positive, other districts are almost negative growth. Furthermoer by means of grey forecasting model to predict the population of Yilan County, in order to propose results to the government for reference when making decision in population policy.