This article studies the current demographic transition in China and its implications on the country's social welfare reform, particularly its Old Age Social Security (OASS) development. The developmental approach is analyzed to examine how developmentalism affects China's social welfare reform. Reviewing the historical development of the OASS system after the 1980s, this article discusses the major issues and concerns under the current system and the challenges it faces for future development. Further studies are called upon to address these issues in order to build a financially sound and socially equitable welfare system in China.