"A failure to act on these issues could have a damaging effect on future prospects, as unemployment rises, the social fabric crumbles, and rising numbers of old people begin to overwhelm available resources. …Embracing and understanding demographic challenges must therefore be a priority for all governments...' (Bloom, Canning, and Sevilla, 2003). And Vietnam had already entered demographic dividend period and this period will be last for the next 40 years, and favorable policies take time to establish and take effect. Investments in education and job creation are vital, as are policies that favor the fertility declines that have created and sustained the window. Therefore, this paper is analysis try to understand age-structure transition in Vietnam; To project age-structure of population to understand future prospect; To study age-structure transition and its implications on demographic dividend/economy.