Continuous and complete population data by age and education level are the basis for studying the dynamic relationship between population and economic and social development in a country or region. However, in non-census years, such data cannot be directly obtained or its quality cannot be guaranteed. To this end, the national population census data from 2000, 2010, and 2020 are used to reconstruct the population data by age and education level for non-census years from 2000 to 2020 using the population discrete development equation forward and backward bidirectional feedback fitting method. Based on this, an improved accounting model is used to calculate the human capital stock from 2000 to 2020.The research results show that the difference between the reconstructed non-census year total population data and the adjusted data from the National Bureau of Statistics is very small. The reconstructed age-specific population data corrected the bias in the age composition data published in previous statistical yearbooks. The calculated data on human capital stock shows that it increased from 15.856 billion person-years in 2000 to 26.479 billion person-years in 2020, with an average annual growth rate of 2.60%. Affected by the ageing population and the decrease in the working age population, the growth rate of human capital stock shows a decreasing trend between the first and the second ten-year periods.