Under conditions of very low fertility,the traditional theory that fertility declines with economic and social development provides little basis or guidance for policies aimed at increasing fertility,and policy measures to encourage fertility in reality show a tendency towards fragmentation.Based on international experience,this paper first points to the existence of a universal fertility level that is the same as the replacement level,and therefore to the general phenomenon of convergence towards that level in both the high and the low directions;it then attributes the factors that have hindered the return of fertility in both history and reality to the problem of weak social mobility;and it concludes by proposing more targeted and effective policy recommendations for raising fertility intentions.