Abstract: Accordings to the Pango nomenclature, a total of 1 379 lineages of SARS-CoV-2 have been identified worldwide as of 20 September 2021. Some lineages have disappeared or are close to disappearing due to the replacement by the variants with higher transmissibility and/or immune escape ability. The World Health Organization (WHO) has defined 4 variants of concern (VOC), 5 variants of interest (VOI) and 11 variants belonging to variants under monitoring (VUM). At present, the Delta variant has replaced the Alpha variant as the predominant global pandemic strain, and it is also the main variant detected in imported cases and local epidemics recently in China. Meanwhile, the Gamma and Lambda variants reported in some countries of South America, the Mu variant reported in some countries of South America and North America, and the C.1.2 variant reported in South Africa have also attracted high attention worldwide. The paper summarizes the variation of SARS-CoV-2 genome and the research progress of key variants of SARS-CoV-2 and put forward the key points of further research based on the spread of SARS-CoV-2 variants.