A novel coronav i rus, SARS -CoV-2, has caused over 85 mi llion cas es a nd over 1.8 milli on deaths worldwide sinc e it oc curred twe lve m onths ago in Wuha n, China. Here we first analyzed 4,013 full-length SARS-CoV-2 genomes from different continents over a 14-week timespans ince the outbreak in Wuha n. 2,954 unique nucleotide substitutions were ide nti fied wi th 31 of the 4,013 genomes rema ining as anc estral type, and 952 (32.2%) mutations recurred in more than one genome. A viral genotype from the Seafood Market in Wuhan featured wi th two concurrent mutations was the dominant genotype (80.9%) of the pandemi c. We also ide nti fie d unique genotypic compositions from different geographic locations, and time-series viral genotypic dy na mics in the early phase that reveal transmission routes and subsequent expansion. In the end, as the pandemic has been unfolding for more than one year, we als o used the same approach to analyze 261,350 full- length SARS-CoV-2 genomes from the world since the outbreak i n Wuhan (i.e. all the available viral genomes in the GIS AI D database as of 25 December 2020) in order to recapitulate our findings in a real-time fas hi on. Our study indicates the viral genotypes can be utilized as molecular barcodes in combination with epidemiologic data to mon ito r the spreading routes of the pandemic and evaluate the effectiveness of control measures .