Objectives: As a unique prevention and control measure, the dispatch of national medical teams to Wuhan has played a key role in protecting Wuhan against COVID-19. This study aimed to quantitatively evaluate the effect of this key measure in reducing infections and fatalities. Study design: A scenario analysis is used in this study, where the forming of scenarios is on the basis of the stages of medical to Wuhan. We divided the evaluation into 4 scenarios: Scenario Ⅰ-no dispatch, Scenario Ⅱ-dispatch of 4,599 medical staff, Scenario Ⅲ-dispatch of 16,000 staff, and Scenario Ⅳ-dispatch of 32,000 staff. Methods: The extended Susceptible-Exposed- Infectious-Recovered-Death (SEIRD) model was adopted to quantify the effect of the dispatch of national medical teams to Wuhan on COVID-19 prevention and control. Results: The dispatch dramatically cuts the channels for the transmission of the virus and succeeds in raising the cure rates while reducing the fatality rates. If there were no dispatch at all, a cumulative total of 158,881 confirmed cases, 18,700 fatalities and a fatality rate of 11.77% would have occurred in Wuhan, which are 3.2 times, 4.8 times and 1.5 times the real figures respectively. The dispatch has avoided 108,541 confirmed cases and 14,831 fatalities in this city. Conclusions: The proven successful measure provides valuable experience and enlightenment to international cooperation on prevention and control of COVID-19, as well as a similar outbreak of new emerging infectious diseases.