The construction of a network of horizontal relations among local governments and the promotion of intergovernmental self-organization exchanges and cooperation are necessary to realize the equalization of public services. Based on a sample of 21 prefectural-level cities in Guangdong province from 2010 to 2019, this article evaluates the different effects of two designed intergovernmental relations—sister-city assistance and the cross-appointment of officials—on the interregional gap in the supply of public services as well as the mediating effect of self-organizing behavior, such as attention to the allocation of public services and study visits on this relationship. The results show that, on the one hand, both types of designed intergovernmental relations promoted by higher authorities can significantly narrow the interregional gap in the supply of basic public services, but sister-city assistance has a more significant, rapid, and sustainable equalization effect on public services. On the other hand, the equalization effect of intergovernmental relations is achieved based on a mechanism adjusting the attention of government to public services and a practical transmission mechanism for more frequent inter-city inspections and exchanges. This shows that the allocation of government attention by local governments and promoted by higher authorities is an effective mechanism to realize the practical governance effects of designed intergovernmental relations. This article provides a comprehensive framework to explain the network of intergovernmental relations and its equalization effects on public services. It also opens up a new analytical approach for the structure-function study of intergovernmental relations based on the “action” of officials' policy preferences.