Abstract: Over the past decade, the power conversion efficiency of perovskite solar cells has increased from 3.8% to the current 25.5%, which is expected to become the next generation of commercial thin-film solar cells. However, the widely used TiO₂ electron transport layer has low electron mobility, requires a high annealing temperature, and has poor UV light stability, limiting the performance of TiO₂-based perovskite solar cells, especially long-term stability. SnO₂ is expected to be the first choice to replace TiO₂ electron transport layers because of its high electron mobility, suitable band structure, low-temperature solution synthesis, and stable chemical structure. Although the certified maximum efficiency of state-of-the-art SnO₂-based perovskite solar cells had exceeded 25%, it was still below its theoretical efficiency. Therefore, component engineering, interface engineering, solvent engineering, and other methods to improve the efficiency and stability of SnO₂-based perovskite solar cells have become a major research focus. Currently, regulating the SnO₂/perovskite and perovskite/hole transport layer interface is key to optimizing the performance of SnO₂-based perovskite solar cells. Most studies focused on improving the charge transport performance of SnO₂ and modifying the SnO₂/perovskite interface, while few studies have addressed defect passivation of the perovskite layer and the modification of the perovskite/SnO₂ interface. Therefore, it is essential to summarize the research progress of interface modification and performance optimization of SnO₂-based perovskite solar cells. This paper introduces the types and characteristics of defects in the bulk and surface of the SnO₂ electron transport layer, as well as defects in the bulk, grain boundaries, and surface of the perovskite film. The research progress of the interface modification (bulk and surface defect passivation) and performance improvement for the SnO₂ electron transport layer/perovskite and perovskite/hole transport layer are reviewed. Finally, the research directions of SnO₂-based perovskite solar cells on interface modification and performance optimization are presented.