The relationship between cities and counties is an important component of the intergovernmental relationship in China, and it is also an important factor in the governance and development of local governments. The shape of the relationship between cities and counties directly determines the shape of the relationship between local governments in China, and is also a factor influencing the modernization of local government governance. In order to adapt to the development of the economic and social system and the construction of the socialist market economy system, the relationship between cities and counties has undergone more significant changes under the dual effects of central policy guidance and local governance reality. To this day, the relationship between cities and counties in China presents a landscape of “city governing counties” as the main approach, compatible with diversified “province governing counties”. However, there are also issues with the relationship between cities and counties in terms of administrative hierarchy, balanced development, and unclear powers and responsibilities. To effectively address relevant issues, by reviewing the evolution process of existing city-county relations, we summarize the external and internal driving forces, and clarify their practical roles in the transformation and development of city-county relations. At the same time, based on the process of change and its driving force, two theoretical divisions have been formed: “city-county integration” and “city-county separation”. Based on this, from the perspective of government responsibilities, relying on the types of affairs, management models, and development directions, we attempt to construct the relationship between cities and counties into four types: completely unified, limited unified, completely separated, and limited separated. We then conclude that the integration of “unity” and “separation” is the main direction for promoting the optimization of city-county relations. Under the determined direction, with government responsibilities as the logical starting point and goal orientation for promoting optimization, we attempt to establish an optimization approach of “innovative concept - construction system - establishment mechanism - promotion synergy”.