ABSTRACT The impact of spatial expansion on innovation performance has garnered widespread attention. This study establishes a two-sector equilibrium model to elucidate the transmission mechanism among urban expansion, human capital and innovation performance. Our findings indicate that the synergy between compact expansion and human capital enhances innovation performance. Drawing from a sample of 281 cities spanning 2005–2018, we observe that Chinese cities demonstrate compact expansion patterns, and human capital fosters the synergy effect of innovation. Furthermore, the synergistic effect of compact expansion and human capital formation is more pronounced in cities with larger populations, higher income levels and stronger regional status. These results offer both theoretical contributions and practical insights for shaping more effective urbanisation patterns and enhancing innovation capacity.