Commercial flights contributed to the early-stage international transmission of SARS-CoV-2. Understanding the effect of international and inter-state flights on virus transmission is important to evaluate the initial response of the outbreak. This study investigated the likely date of the emergence of the first COVID-19 case. We constructed a geographical-structured epidemiology model, integrating 2541 province-level units, 250 country-level units, and 26,094,036 flight plans to evaluate the possible date of the emergence of the first case. Using the model, we estimated the number of cumulative deaths and the date of first death caused by COVID-19 in different countries. The pattern of the three parameters we evaluated suggests a high likelihood of the emergence of the first case of COVID-19 be around September 15 and September 22, 2019.