The fall armyworm, Spodoptera frugiperda, is a globally significant invasive pest that has spread rapidly across China’s major grain-producing regions since it was first detected in 2018, and that now poses a severe threat to national food security. This review systematically summarizes recent advances in research on the biotypes and population genetic diversity of the S. frugiperda, and discusses the implications of this research for the integrated pest management (IPM) of this species. Previous research indicates that the S. frugiperda in China is primarily comprised of corn and rice strains. Invasive populations are predominately the corn strain, but there is widespread hybridization between the two strains. This hybridization leads to inconsistent identification using conventional molecular markers (e.g., COⅠ and Tpi), highlighting the need for alternative, more definitive, molecular techniques. Genetic analyses reveal that there was low initial genetic diversity in Chinese S. frugiperda populations, but that this increased over time due to migration and hybridization. Invasive populations mainly originate from Southeast Asia (e.g., Myanmar and Vietnam), and follow an “advance southward and expand northward” expansion pattern. Adaptive evolution, including the expansion of gene families such as CYP450 and GST, has enhanced the environmental adaptability of the species, including its ability to detoxify pesticides, contributing to the development of insecticide resistance and host shift potential. Future research should integrate multi-omic technology and high-resolution markers to elucidate the mechanisms underlying these kinds of adaptation and resistance, and establish an international genomic platform to support sustainable management strategies against the S. frugiperda.