Understanding the demographic changes and inferring future population development is an important basis for social and economic planning and development decisions. Grey system analysis means to analyze the stability and development trend of the system based on grey system model. According to the population data of Taipei city from 2013 to 2017 and by means of grey system analysis, we found that the population growth mechanism in Taipei city is very stable. The average relative error of the population predictions of the original system and the two subsystems is small. In addition, the predicted population of Taipei City in 2021 is 2,660,923. The results can be provided to the government department for reference when generating the policy of population development or making the input measures of public utilities.