Based on the figures obtained from a survey carried out in Nam Dinh, Thua Thien-Hue, and Dong Nai Provinces, and Ho Chi Minh City by the Vietnam Academy of Social Sciences (VASS) in 2019-2020, this article analyses the factors affecting the replacement fertility in Vietnam following the Bongaarts model. The results indicate that the country’s replacement fertility is currently in a state of flux under the combined impact of the expectation of having two children on average, the group of traditional fertility increasing factors, and the group of fertility decreasing factors. To sustain the replacement fertility, it is necessary to strengthen communication so that a two-child family can become the standard model for society as a whole. In addition, social security solutions and policies need to be applied to mitigate factors that increase and decrease the birth rate, thereby creating favourable conditions for individuals and families to realise this standard model.