Ever since the first session of the United Nations Environment Assembly (UNEA-1) in 2014, the field of eco-innovation in small and medium-sized enterprises (SMEs) has received unprecedented attention. However, knowledge analysis in this area still needs to be better developed. By using bibliometric methodologies, this study seeks to establish a thorough framework for knowledge analysis to compare the research dynamics of eco-innovation in SMEs between pre- and post-2014. We thoroughly investigated 1996 records in the Web of Science database using CiteSpace, VOSviewer, and other applications for visualization and analysis. The study found that research on eco-innovation in SMEs has shown significant growth since the UNEA-1, with the leading country changing from the United States before 2014 to China after 2014. Second, the study reveals the evolution of the knowledge structure. Taking 2014 as the classification node, research on eco-innovation in SMEs has evolved from corporate entrepreneurship and environmental management in the early period to sustainable entrepreneurship, the circular economy, and digital transformation in the later period. The hot topic of study progressively transitioned from a singular technological aspect to a multifaceted innovation encompassing organizations, procedures, services, etc. Finally, this study identifies directions for future research, such as combining ESG development needs, improving the diverse effects of different types of SMEs, and developing eco-innovation pathways for SMEs in the Industry 4.0 era. This paper provides researchers, policymakers, and the business community with an in-depth understanding of the knowledge structure and research frontiers of eco-innovation in SMEs.