Social security and high-quality economic development are important ways to achieve common prosperity. At the present stage, Chinese economic development has shifted from high-speed development to high-quality development. However, social security sustainability has been challenged by demographic transformation, which has an impact on the sustainability of economic development. It is also bound to further affect the coordinated relationship between social security and high-quality economic development. This article constructs an analytical framework for social security and economic high-quality development based on system theory. On the basis of elaborating the theoretical relationship between social security and high-quality economic development, the quality of social security and the index of high-quality economic development are comprehensively measured based on Chinese provincial panel data. The dynamic relationship between social security and economic high-quality development is also analyzed by using the decoupling theory and the coupling coordination degree. It is found that: first, both the quality of social security and the index of high-quality economic development show an increasing trend year by year. The indexes of social security quality and economic high-quality development are higher in provinces with faster economic development. However, in terms of the index growth rate, the economic quality development index of most economically backward regions grows faster than that of the economically faster developing regions. In contrast, the growth rate of their social security quality is slower than that of regions with faster economic development. This finding reflects that the quality of social security and the quality of economic development are not synchronized within regions. Second, the relationship between social security and high-quality economic development as a whole is characterized by decoupling, negative decoupling and fluctuating linkages, with the dominant decoupling showing a “progressive deterioration”. The high-quality economic development of each province mainly shows the trend of inefficient expansion. Third, the degree of coupling and the degree of coupling coordination of the two systems have both been on the rise year by year. However, they are still in a low state of coordination. Fourth, in the heterogeneity analysis, the system coupling and coordination degree of social security and economic high-quality development shifted from barely coordinated to primary coordinated in the eastern region. The central region evolves from on the verge of dysfunction to barely coordinated. In the western region, the degree of coordination of the system coupling between social security and high-quality economic development has evolved from mild to imminent coordination. All in all, the government needs to reasonably grasp the “appropriateness” of social security. And on the basis of making a bigger cake, it should share the cake well, so as to ensure that social security and the economy can achieve high-quality development on the basis of coordination and sustainability. Compared with the previous literature, this paper expands in the following two aspects: first, in terms of the selection of indicators, it is different from the existing studies that measure the level of social security only from the level of expenditure. This paper measures the quality of social security from the expenditure, income, coverage to collection of social security items. Not only the “quantity” but also the “quality” of social security is taken into account. Secondly, the mechanism of coordinated development between social security and high-quality economic development is analyzed on the basis of Luhmann's social system theory. It expands the relevant literature from a new perspective, and further measures the degree of coordination between the two. Through the results of the measurement, it finds the problems existing in the relationship between social security and economic development at the present stage in China, which will help the relevant departments to put forward reform measures. [ABSTRACT FROM AUTHOR]