Rural-urban integration development is an inevitable requirement of Chinese modernization，and the key and focus of China’s rural-urban integration development lies in the county-level units.This paper constructs an evaluation index system for county-level rural-urban integration development，measures the level of rural-urban integration development in 1 451 counties in China from 2015 to 2023，and analyzes its regional differences，dynamic evolution characteristics，and driving mechanisms.The study finds that: The overall level of county-level rural-urban integration development in China has increased，presenting a spatial gradient pattern of “high in the eastern and central regions，and low in the western and northeastern regions”.The average annual growth rates in the central and western regions are faster than those in the eastern and northeastern regions; internal differentiation in the eastern region has intensified，while the degree of internal differentiation in the central and western regions is relatively small; inter-regional differences are mainly concentrated between the eastern and northeastern regions，as well as between the eastern and western regions，while the differences among the central，western，and northeastern regions are relatively small.At the national level，marketization，agricultural modernization，industrialization，and government behavior all play a significant role in promoting county-level rural-urban integration development，but their influence intensity decreases in turn，with obvious heterogeneity in their effects across the eastern，central，western，and northeastern regions.Therefore，giving play to the role of a proactive government，implementing differentiated regional economic policies，and promoting the coordinated development of marketization，industrialization，and agricultural modernization are effective ways to promote the high-quality development of county-level rural-urban integration in China.