At present, China has entered a low-fertility society, and the continuous low fertility rate and the labor supply structure problems caused by it have attracted increasing attention. Theoretically, the equalization of income distribution and the strengthening of social security to support fertility will promote an increase in fertility. However, the existing literature lacks empirical analysis on the impact of income distribution and social security expenditure on fertility in the low fertility stage. The fertility transition from the high-fertility stage to the low-fertility stage is mainly due to the change of people’s concept of fertility from the pursuit of fertility to the pursuit of fertility quality, and the continuous increase in fertility costs caused by the pursuit of fertility quality has become one of the important factors that inhibit fertility. In particular, the fertility behavior of low-income families is subject to greater income constraints, so their actual number of children is lower than the potential willingness to have children. The equalization of income distribution not only reduces the proportion of low-income families in the whole society, but also reduces the income constraints of low-income families’ reproductive behavior by narrowing the income gap, thereby promoting the overall fertility rate; based on people’s demands for high-quality fertility and the goal of optimizing the structure of labor supply, the improvement of social security that strengthens fertility support will reduce the average fertility cost of society, thereby promoting the overall fertility rate. The EU entered the low fertility stage earlier and there was a certain fertility recovery, this paper takes the 27 EU countries from 2000 to 2020 as a sample of empirical analysis and finds that on the whole, the Gini coefficient of the sample countries is significantly negatively correlated with the total fertility rate, while social security expenditures are significantly positively correlated with the total fertility rate; as the total fertility rate increases, the promotion effect of the Gini coefficient reduction on the increase in the total fertility rate has changed from not significant to significant and continues to increase, while the promotion effect of increased social security expenditure on the increase in total fertility has been significant at different fertility levels; the impact of Gini coefficient and social security expenditure on the total fertility rate has a mutually reinforcing interaction effect, that is, the decrease of the Gini coefficient will strengthen the promotion effect of the increase of social security expenditure on the increase of the total fertility rate, and the increase of social security expenditure will also strengthen the promotion effect of the reduction of the Gini coefficient on the improvement of the total fertility rate. Compared with the existing literature, this paper expands and deepens this study mainly from the following aspects: on one hand, the empirical analysis in the EU region provides empirical evidence that the equalization of income distribution and the improvement of social security can significantly promote the increase of fertility in the low-fertility stage; on the other hand, through quantile test and interaction effect analysis, the mechanism of Gini coefficient and social security expenditure affecting total fertility rate was further clarified. This paper reveals that in the low fertility stage, the fertility rate can be increased by adjusting income distribution and improving social security, which is conducive to the realization of high-quality fertility and population development in the promotion of common prosperity. On the basis of providing material guarantees for the continuous improvement of fertility quality through high-quality economic development, we should continue to narrow the income gap and increase fertility support, thereby effectively increasing the overall fertility rate.