Abstract: The reforms to "streamline administration and delegate power, improve regulation, and upgrade services" play an important role in optimizing regional business environment and enhancing competitiveness of cities. However, there are few empirical studies on the effect of the reforms. Based on the panel data of 35 prefecture-level cities in China from 2015 to 2018, this paper conducts an empirical study on the relationship among the reforms to "streamline administration and delegate power, improve regulation, and upgrade services", the regional business environment and competitiveness of cities by means of ordered multiple logistic regression analysis and multiple linear regression analysis. The results show that the implementation of the reforms to "streamline administration and delegate power, improve regulation, and upgrade services" and the construction of government service centers can significantly improve the regional business environment and enhance thecompetitiveness of cities, but the construction of government service centers has a more significant effect. In addition, the regional business environment plays both a mediating role and a positive regulatory role amongthe implementation of the reforms to "streamline administration, delegate power, and improve regulation, and upgrade services", the construction of government service centers and the competitiveness of cities. The implementation of the reforms and the construction of government service centers have the most significant impact on institutional competitiveness, while the regional business environment has the most significant impact on the talent competitiveness, and the implementation of the reforms to "streamline administration and delegate power, improve regulation, and upgrade services", the construction of government service centers and regional business environment have a more remarkable positive impact on the competitiveness of cities in the eastern region.