Based on panel data of Chinese provinces from 2011 to 2020, this paper presents empirical research on the quantitative relationship between China’s national quality and sustainable development. Moreover, this research is implemented under the index system of national quality competitiveness. Firstly, a system for assessing national quality level is established, and the factor analysis method is applied to comprehensively analyze each province’s national quality; this produces a national quality score for each province. Secondly, an Index of Sustainable Economic Welfare (ISEW) and calculation methods are created. Thirdly, the Pearson Correlation Coefficient is employed to explore the relationship between the national quality of Chinese provinces and the sustainability of their economic development. Finally, the test of Granger causality (panel data) is applied to further analyze the interplay between national quality indexes and sustainable economic development. As the research results indicate, national quality can comprehensively impact sustainable economic development at any economic level, as well as its sustainable capability. National quality can still comprehensively affect the sustainable development of the economy. Nevertheless, sustainable economic growth does not affect all elements of national quality, especially at the level of morality. Additionally, the positive influence of sustainable economic development on national quality is limited and lags behind. Based on the results of our empirical analysis, several policy recommendations are given to improve China’s national quality and sustainable economic development.