In order to enrich the empirical evidence of the impact of university agricultural science and technology extension on high-quality agricultural development, and explore effective ways to promote high-quality agricultural development, the “Construction Plan of New Rural Development Institute of Colleges and Universities” launched in 2012 in China was regarded as a quasi-natural experiment, and the relevant panel data of 188 counties in Jiangsu, Hunan, Anhui and Zhejiang provinces from 2010 to 2019 were selected for empirical analysis using the difference-in-differences method. The study finds that, (1) University agricultural science and technology extension has a significant positive impact on high-quality agricultural development. (2) Urging the government to increase financial support for agriculture and improve land productivity are the important reasons for positive impact of university agricultural science and technology extension on high-quality agricultural development. (3) Universities directly under the Ministry of Education have a more significant positive impact on high-quality agricultural development than provincial universities. The impact of university agricultural science and technology extension in areas with moderate agricultural development foundation on high-quality agricultural development is more obvious. Compared with the resource combination type of universities and local governments, university agricultural science and technology extension based on the resource combination type of universities and enterprises has a more significant positive impact on high-quality agricultural development. The research findings provide policy implications for improving the operation mechanism of agricultural science and technology extension of universities and promoting the high-quality development of local agriculture under the background of rural revitalization, such as expanding the coverage of agricultural science and technology extension of universities, creating external conditions suitable for universities to carry out agricultural technology extension services, comprehensively strengthening the ability of universities to serve local agricultural development, and strengthening the deep integration of universities, regions, schools and enterprises.