Small cell lung cancer (SCLC) is a cancer with high heterogeneity and malignancy, and has a high incidence rate and mortality worldwide. Owing to the strong concealment of early metastasis, diverse cell types of origin, and complex mechanisms of metastasis, further in-depth research is needed on the potential mechanisms of metastasis. It is particularly important to elucidate the heterogeneity of tumor cells, the tumor microenvironment, and intercellular communication networks. Traditional high-throughput sequencing methods provide an average measurement of gene expression, but cannot capture the “heterogeneity” between cells and affect the accuracy of gene function knowledge. In contrast, single-cell sequencing technology allows for amplification of the entire genome or transcriptome at the single-cell level, enabling unparalleled accuracy in examining gene structure and expression. This method provides valuable insights into disease mechanisms and can identify changes in transcription factors associated with SCLC. In addition, it revealed different cell populations and their unique roles in the tumor microenvironment, providing a comprehensive understanding of the cellular landscape that supports the pathogenesis of SCLC metastasis. This review focuses on the research of single-cell sequencing technology, on the possible mechanisms of metastasis in small cell lung cancer, and discusses the challenges encountered in current lung cancer research.