Vigorously developing digital economy has been elevated to a national strategy, and the digital economy is gradually becoming a core driving force to promote high-quality economic development, which is a key area concerning China’s industry, economy and national security. This study analyzes the direct impact effect of the digital economy to promote the high-quality development of the regional economy and its internal mechanism of action, namely the consumption expansion effect. It further conducts an empirical study based on measuring the development level of the digital economy at the provincial level from 2013 to 2020. The results show that the digital economy can significantly contribute to the high-quality development of the regional economy, and the relationship between the two is in an inverted “U” shape. Therefore, in the process of developing the digital economy, it is necessary to avoid harm and expand moderately according to the spatial and temporal characteristics. The role of the digital economy in promoting high-quality regional economic development is more prominent in the central and western regions, while there are also significant differences among the five economic zones. Further, the expansion of consumer demand and consumer supply is the intrinsic mechanism of action of digital economy to influence the high-quality development of regional economy. The research results provide empirical evidence for deepening the digital economy to promote regional economic high-quality development.