Eight new age groups，distributed in 5-year intervals，were noted at the bottom of the age—structure pyramid of China’s population to the 40th anniyersary of the People’s Republic. The uneven distribution of population within the groups will exert a crucial impact on future population development. Although each age group has its own impact，the birth peak that occurred between the early 1960s and the early 1970s，and two following peaks，to be referred to as the “third population boom” in this essay，deserve the most attention，due to China’s problem of surplus population. This problem is the key to China’s long-term population growth.